Ranging / about screen / pull to refresh

- Implemented pull to refresh
- Write the new default TX power value
- Show the about screen at first launch
- Updated uribeacon library

I used the same function name as in `android-uribeacon/uribeacon-library/src/main/java/org/uribeacon/scan/util/RangingUtils.java`, line 129 to be consistent.
Should I change that anyway?