Revised for ASUS Transformer tablet

fixed an IndexOutOfBound error
Minor fixes

1. Fix redundant startentries by adding re-initialization in "Start"
onClick function;
2. Added "Cancel" button and fallback function;
3. Experiment time interval: 5min to 3min;
4. Added a prompt for GPS.
Time attribute updates

1. TimeAfterBoot attribute changed to absolute UTC timestamp;
2. Added dtime attribute to SAT and LOC tables: elapsed time after start
of experiment.