SD Card implementation

[oscgonfer]

So the SD card library was upgraded in dev branch with refurbishment and new features. These issue is to map the overall status of this improvement, the sd-card library implementation and overall sd-card handling status.

Specially in sd-card (offline) mode it can lead to a warning or a more critical data loss if/when flash memory runs out.

This is also linked to the new CSV handling also included in that commit, which now has a "hash" check for the CSV header. This is done so that (dis)appearing sensors don't mess up with the current files. Also, there are some TODOs to consider in https://github.com/fablabbcn/smartcitizen-kit-21/blob/dev/sam/src/SckBase.cpp#L1252-L1253

In general, an overall review of the implementation with possible cases is necessary taking into account:

• Check stability of the new library
• Check implementation of csv header hash, naming...
  • Flash system and the particularity of old data posted after sd-card insertion (currently it doesn't check that data is saved in not a chronological order, but it works fine)
• Check filesystem utils working OK (for instance to pipe the files to terminal output)
• No wipe is implemented but that's fine for now. Good to have maybe for the future
• In principle no other pending TODOs

[oscgonfer]

In principle this is more testing than anything else.