Issue 60 support for gzip header

Adds optional `Accept-Encoding: gzip` header to JSoup's connection requests:

- Create `/application/MainApplication` class that serves as an Application instance; get context from anywhere in code
- Modify settings page; add "Compress Data" option
- Modify `/data/ConnectionManager.java` and `/fragment/WebFragment.java` to read user preferences to determine if response data should be gzipped or not