Add command line option for kreon

Resolve CRTP specific function name

Testing Infrastructure for different databases

add path

Reactivated destructors, kreondb is destroyed to reduce CI space

Returning string_view in fs_data added dbbackend property

Updated Readme and MetatadaFactory

Adding extra options for kreondb, README+CHANGELOG updated

Update .gitlab-ci.yml

updating script test...

Updated dl_dep tests

Kreon test (for metadata) backend.

Add command line option for kreon

Resolve CRTP specific function name

Testing Infrastructure for different databases

add path

Reactivated destructors, kreondb is destroyed to reduce CI space

Returning string_view in fs_data added dbbackend property

Adding extra options for kreondb, README+CHANGELOG updated

updating script test...

Updated dl_dep tests

Remove Kreon - Add Parallax

Add Parallax

Add DockerFile

adding parallaxdb option

Docker update

Missing Parallax hpp

Removed Kreon from code, lib conflicts

Updated Parallax master

Updated DockerFile deps

Reformat

Changed Base

Added ps

Reduced Logging and added ps in docker

Add Path

increase testing timeout

Create options.yml automatically

Updated out tests

Client now reads host file to determine auto_sm and RPC protocol

gkfs::hg_tag -> gkfs::rpc::tag
gkfs::utils -> gkfs::util
gkfs::client -> gkfs::util
gkfs::logging -> gkfs::log

Reformatted code w.r.t. unifying code styles as of the official
CPPCoreGuidelines by Stroustrup and Sutter

Restructuring code w.r.t. configurations and definitions:
- #defines have been mostly removed from configurations
- a dedicated config file has been added for configurations with constexpr
- past configure file is now only a cmake wrapper
- wrapping global functions into namespaces

Removed all adafs and ifs occurrences. Now called gkfs

 - Use regular expression to parse lines
 - More consistent error handling
 - More comprehensive error messages

We now use getaddrinfo syscall instead of parsing /etc/hosts in order to
resolve hostnames

For some comunication layers an out of band communication is required for putting in place the specific protocol handshake.

In those case a shared lookup file could be used to distribute deamon's endpoints information to all the clients.

This file need to resides on a shared filesystem and can be specified using the new CLI parameter `--lookup-file`.

The access RPC have been removed. The POSIX access functionality now is implemented through the stat RPC. This makes code easier to maintain and modify.

There would be a little performance degradation on the POSIX access
function because we are now retrieving also the metadata
associated to the file.

This change makes a lot easier to add symlink support

 - improved statfs system call
 - intercepted statvfs library call

Both of the above function now report the aggregated real size
of all the data-nodes.

You can test this with `df "/tmp/gekkofs_mountpoint"` command

the functionality wasn't used at all and it will be implemented later
with a different approach

Some of the variables of stat struct are not initialized, thus they will
remains will unpredictable junks data from memory. This random values
could induct strange behaviours on user applications.

Even if we don't support some of the fields in the struct stat, it is
necessary to set them to some default value.