Allocation of Lookahead bitmap

[CasperBroekhuizen]

Most functions now work asynchronously, in order to not trigger the WDT on write.

The current strategy is to keep a minimal amount of files, but appending the telemetry to really big files
(probably one file every 24hours)

On a reboot, the freeblock bitmap lookahead is lost, regenerating that will require traversing all the programmed blocks on the device and is very time-consuming. mitigation should be found. (issue 75 on lfs git). Maybe store the lookahead on the SDcard / FRAM.

[CasperBroekhuizen]

Some mitigation committed in 026ab62

Increasing the blocksize will decrease the number of blocks allocated, hence making the traversal faster.