New sending option - "Email location"

Using previous location to send coordinates if the current location is not available
(logging is stopped).
Adding timestamp variable in message template, changed default template.
Bug correction: new line in template is correctly processed now.
Zipping files (if supported and configured) when sending manually, added 'acceptZip' function to upload helpers.
Monitoring of battery level is added - stop tracking if the level is below critical
Bug correction - startup of app with battery discharged
Replaced system icons in menu, added two icons for import/export settings
bump version, bug fix in livetrack24, simple tweak in igc logger
Merge branch 'master' of https://github.com/Peter2121/gpslogger
bug fix #9 "livetrack24 bad ending"
simple race cond between location in the buffer and the end packet.
Stop sending packets when 'STOP' has been hit. We should wait for the buffer to be empty before sending the END packet...