Save and store last log file directory

and reuse it when loading or saving new log files

Fix/Revert problematic logfile structure changes

The reason for this is, because the last change in the file structure is buggy, it was only written the message length of the buffer to the file and missed to add the length for the timestamp.
For fixing this problem it would be possible to insert something like

len += sizeof(quint64);

after:

int len = mavlink_msg_to_send_buffer(buf+sizeof(quint64), &message);

But I think a consistent file structure has more adavatages for a logfile over a more compressed structure.
E.g. it would be necessary to go through all packages to proceed a jump during a replay.
Additional the LogPlayer was not updated during the last 7 month since the logfile structure was changed (even it was buggy)...

If filesize is really a problem I would recommend to change the logfile handling in a way of writting a temporary consistend
logfile and compress it afterwards (QCompress) like done by many programs

fix hardcoded start of fgfs and terrasync, use system environment variables for linux distro independence

First stab at JSBSim interface, compiling, operational, but needs the correct startup folders and arguments

fix hardcoded start of fgfs and terrasync, use system environment variables for linux distro independence

archlinux compatibility

First, stupid, naive version of PX4 uploader, needs testing and cross-platform fixes. Compiles, ready for testing