Bug fix and refactoring of globalTimer

After reading this post http://www.rcgroups.com/forums/showpost.php?p=28810543&postcount=2197 Ilooked at the code and spotted:
* g_eeGeneral.globalTimer was not saved to EEPROM after reset, session timer reset was also missing
* noticed duplication of session timer: `s_timeCumTot` and `sessionTimer` both did the same thing, so I removed one.

Please review and merge if ok.