semcomedi: avoid dead-lock when waiting for a thread that has just started to finish

acquisition thead uses data_lock, so it can dead-lock if you wait for the thread
to finish while holding this lock.

The solution is to differentiate between modifying data and manading the thread,
via 2 different locks.
gui: use log scale instead of cubic scale for time-based values
semcomedi: less verbose
gui: refactor text ctrl to be simpler to handle

The main behaviour changes are:
 Get/SetValue() return/receive a number, that is the last validated one
 Get/SetValueStr() should almost never be called and set the current text
 When not on focus, the number is display as pretty as possible
 It's tried much harder to make any use of the new value typed by the user
 SetValue doesn't generate an event

The main advantage is to get beautiful numbers displayed by default.
It also reduces the chances of infinite loop between changing the value from
a VA and on the GUI.