logview: always pickle the framed log data for faster reload
uavtalk.py: format data correctly for overo logs too
Python: convert timestamps to seconds

The log files all use millisecond for the timing precision. This
converts to double seconds when unpacking this value into the
UAVO itself. This format is much more convenient for any analysis
and being a double avoids nasty effects when visualizing as
time.
logview: delete large obsolete variable to reduce memory footprint
Merge pull request #1149 from solidgoldbomb/python-logview-speedup

logview: always pickle the framed log data for faster reload