Allow Description Field for Logs

[famo]

In the logging page of the app we need a field to enter a description (or comment if you will) for the next recorded log. The text of this field will then be saved in the header of the log, e.g.

PCB: 007
ASM: 000
LOT: 00000
FW: 1477971088
CH1: AMPS 10A
CH2: VOLT 60V
SMPL: 0064 0125Hz
DESC: --> THIS HERE IS THE NEW DESCRIPTION FIELD!!!
UTC TIME SEC ,CH1 AMPS DC ,CH2 VOLT DC
1501494691.885, 0.000000E000, 3.549508E001
...
The position doesn't matter, but it would be nice if you could take over the "DESC: " indicator, since I have already a script for that.

Background:
I'm measuring different but similar devices (e.g. battery #1 to #4). However I cannot immediately transfer these logs (which span some hours) to my pc. So at the end of the day, I have problems assigning the logs to the respective battery w/o handwritten notes.

[famo]

BTW:
Here is a sclilab script I wrote which already makes use of the DESC field:
https://moosh.im/f/topic/scilab-script-for-visualization-of-mooshimeter-log-files/