There are many ways of iterating over lists in C++/Qt.
In the specific case of QStrings, it is known [1] that using
foreach with const references avoids the creation of new
QString objects in each iteration, reducing the time consumed
by the loops.

[1] https://blog.qt.io/blog/2009/01/23/iterating-efficiently/



Signed-off-by: Anselmo L. S. Melo <anselmo.melo@intel.com>

Moving methods from MainWindow to QGCApplication so that more things
can run without a window. Helpful for testing.

Refactored the LogCompressor. It wasn't properly handling certain message logging files that mixed messages (Issue #70).
One note is that this logger should work correctly as I've tested it, but could have some edge cases. It is pickier about the file format that it will sparse, but I don't know if the error-checking stuff from the old code would have actually worked. This can also be easily re-added.

This code is also much faster than the old stuff. From what I could tell it scanned through the log file at least twice, I think three times. It also copied a lot of data into memory instead of reading, processing, and writing one line at a time, so memory use should be much lower. Some memory leaks from the old code were also refactored out, so lifetime memory use should be down.

Significantly improved logging precision, added hole filling for missing data points (user-preferences for this still pending)

Improved line chart, brought back movement on HUD (but still looks somewhat wrong on the dials). Fixed logging for ground time mode

Fixed SLUGS related warnings. Commented the visibilityChanged connection (MainWindow.cc 535) because it does not take into account when the widget is hidden when changing perspective. Will work on a fix

Significantly improved plotting, now capturing data in linechart allows limmediate processing / analysis of the whole flight