Extension: Enable seg=N and surf=N in long_fastsurfer

[dkuegler]

Make long_fastsurfer.sh support --threads seg=X and --threads surf=X notation bx fixing/adding support to long_prepare_template.sh

Add messages to parallel longitudinal processing to make waiting more clear Fix some variables in long_fastsurfer.sh

These flags were introduced in #640

This is tested and works as expected.

[dkuegler]

This still currently has two (minor) issues:

1. Longitudinal surfaces are not in-fact parallel but sequential.
2. During longitudinal surfaces (in parallel mode) all run_fastsurfer log lines are doubled

[dkuegler]

Well, turns out both of these seem wrong. In fact, there is only a bug in brun_fastsurfer.sh that does not prefix the subject id correctly making it seem like double-logging of messages from one case. In fact, it is Single-Lifting two parallel processes :face-palm:

So in reality, I just need to fix this logging issue.

Independent of that, I think I should probably take a look at the log files as well and see if they can be deciphered as is or if the logging of parallel processes makes them impossible to read...

[dkuegler]

All issues are fixed