StatSummarizer and SummaryListener are based on the same-named classes from the
routerconsole. Data is stored in memory using an AndroidPlot SimpleXYSeries.
Only the last 30 points are currently stored.

A WebActivity has been added back to encapsulate the web browser functionality,
allow the nav drawer items to be launched and enable other fixes.

Broken: cannot find net.i2p.i2ptunnel.I2PTunnel
(but it can when launching the router)

Temporary; will eventually be in an about menu in settings

The navigation drawer has been (mostly) migrated to link to Activities instead
of Fragments. Only Activities can be searched via the inbuild Android search
function, which uses Intents.

Side-effect: some constant strings are now public

- Migrated I2PActivityBase and subclasses to Fragment
- Added new MainActivity with navigation drawer to handle Fragments
- Added MainFragment to navigation drawer

Code compiles, installs and runs. Known bugs created:
- Some buttons now fail (can't use an Intent with a Fragment)
  -> Migrate usage of Intents to Fragment transactions
- New install/upgrade dialogs are commented out
  -> Migrate old Dialogs to DialogFragments