Compile for host

[mrquincle]

Features:

• Supports new Nordic SDK (17.1.0) compared to current SDK (15).
• Supports new Softdevice (7.2.0) which comes with this SDK.
• Supports new nRF52840 hardware (which requires more up-to-date SDK or rather softdevice).
• Supports compilation for tests files for hosts through the implemented -DCOMPILE_FOR_HOST cmake option.
• Supports automatically running of those tests through github actions through ctest.
• Bug fixes (e.g. to support older CMake versions) around the use of csutil and make write_config which are helper tools for getting a Bluetooth address using nrfjprog and subsequently setting up the Crownstone without the need for a smartphone.
• Removed (the need for) patches by pulling in code through (patched) repositories.
• All necessary patches have been applied to https://github.com/crownstone/nrF5_SDK/tree/17.1.0 (the 03nrf4.patch is not necessary).
• Added Mesh SDK 5 (we are now at 3). Reapplied most patches except for the one on persistence of mesh information external to the mesh.

TODO / Recommended:

• Reapply persistence patch to Mesh SDK 5 (considered new PR).
• Mesh functionality is not yet tested on the nRF52840.
• The code base has all flash and ram options set properly for the nRF52840, but pin layout of new prototypes is yet unknown and also has to be tested for development boards.
• A fork of the Nordic SDK which compiles for host is being maintained at https://github.com/mrquincle/nrf5_sdk under branch host. When this become more mature it can be placed under crownstone custody. The purpose of this branch is to step by step (1) allow any Nordic file to be included from the host without compilation issues and (2) provide dummy functionality through emulation. Similar to e.g. compiling bluez with --enable-testing.
• Just a few host tests are "in there"

[mrquincle]

@vliedel All remarks have been considered and addressed.

[mrquincle]

Mesh patches have been reapplied to 5.0.0 at https://github.com/crownstone/nRF5-SDK-for-Mesh/tree/5.0.0 except for the patch that's about implementing persistent storage outside the mesh itself: https://github.com/crownstone/nRF5-SDK-for-Mesh/commit/8d4135bbe9680ed6394943175399db5608f4d293. The file net_state.c has changed too much. There's backwards compatible persistence implemented when the proper flags are set in mesh_config_flashman_glue.c. This patch is considered to be not part of this PR and needs to be applied to https://github.com/crownstone/nRF5-SDK-for-Mesh/tree/5.0.0.

[mrquincle]

@vliedel Defaults are as described in https://github.com/crownstone/bluenet/commit/ba599bedcfcd1b796b18ed8021cd3579ed63f612. Should now be ready for acceptance.