Rename gem::rpc to gem::hardware

Description

This MR aims at improving the GEM code structure by renaming gem::rpc to gem::hardware. However, most of the changes come from other uniformization improvements:

• Unify the harder guards (were an agglomerate of different conventions previously)
• Add the gem::hardware namespace (was non-existing before)
• Make sure that the header file corresponding to a given source file is included first

In addition, some more cleanups were implemented:

• Use a unique log4cplus logger in gem::hardware, initialized at the same time as the rest of the logging
  • The logging system must now also be initialized in the standalone applications
• Remove the legacy vfat_parameters map
• Delete the gem::hardware::fw_version_check function
• Replace the usage of the NUM_OF_OH register by the gem::hardware::amc::OH_PER_AMC compile-time constant
• Suppress a useless VFAT out-of-sync logging statement in monitoring RPC method

Related Issue

• Will help in writing the documentation asked in #145
• Remove the xhal namespace from gem::rpc/gem::hardware as proposed in #111

How Has This Been Tested?

Able to recover the back-end board and start a run on gem904daq04.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.