The onPause() method in SettingsFragment was removed as it is unnecessary. The
parent SettingsActivity onPause() is sufficient to save config changes.

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.

Refreshing is now disabled in PeersFragment and WebFragment, but both of them
will eventually be removed.

All page logic is in the Fragments. Activities don't need the convenience
methods.

zzz and sponge pointed out that the router needs to be managed by whatever
Activity happens to be active (in case an automatic start is required). This
commit reverses the initial migration of I2PActivityBase to a Fragment (code is
broken now).

There are a lot of changes here:
- The main_content FrameLayout is now main_fragment (more logical name).
- TunnelEntry now stores a Context instead of a TunnelEntryLoader (so
  it can be instantiated inside the detail Fragment).
- The activity_navdrawer layout is now an alias to a one-pane or two-pane
  layout depending on screen size.
- Subclasses of I2PActivityBase can now override canUseTwoPanes() to enable
  and use the two-pane layout (for devices that support it).

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