Resolve "Add ofi+verbs support"

Closes #98

See merge request hpc/gekkofs!38

Resolve "ls broken on some systems"

Closes #85

This is partly a revert to previous functionality which was removed during code maintenance, but so that the modified `linux_dirent` struct is only used in `gkfs_functions.cpp`.

Also some comments added.

See merge request hpc/gekkofs!35

Resolve "#endif misplaced if we don't use symlinks"

Closes #86

See merge request hpc/gekkofs!36

Resolve "pwritev: Operation not supported"

Closes #82

See merge request hpc/gekkofs!34

Signed-off: Marc Vef

02 20 code maintenance

General code maintenance:
- remove dead code
- remove as many `#define` as possible and use `constexpr` instead
- remove adafs occurrences and replace with gkfs
- reformat code to unify code style as of CPPCoreGuidelines
- rearrange imports, remove unused imports
- separate cmake configurations and FS configurations
- encapsulate non-prefix gkfs functions into namespaces
- change copyright statement to 2020
- cleanup of some irrelevant code and unnecessary struct definitions
- consistent renaming for rpc sender functions and create and remove functions from client to daemon
- encapsulate all code into namespaces even if naming and structuring is tentative

See merge request hpc/gekkofs!31

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

to avoid name clash with rpc types

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

Resolve "[Mogon II] Fix dependency compilation scripts"

Closes #45

See merge request !25