Add a settings to disable WebView switching.

WebView switching was added in Android 0.7 to fix a bug with custom
fonts on some versions of Android. However, recent versions of Android
seem to have fixed this issue.

This commit adds a setting to force quick updating of WebViews, so that
we can ask users to test this on a number of devices with the next
release and see if this is still an issue on any device.

Hopefully, we can identify which versions of Android we can disable the
workaround by default and possibly remove the setting in future
versions.
Merge pull request #18 from flerda/v2.1-recreate-webview

Add a settings to disable WebView switching.
Fix CSS in Reviewer for the default font.

The CSS used for the default font was actually invalid because a number
of things were missing or incorrect.

This should reformat and fix the CSS.
Saving the content of the cards.

This commit adds a flag to Reviewer.java that allows to same the content
of the cards. This can be quite useful for debugging purposes.
Use ruby tags and styled spans for furigana instead of CSS tables.

Make use of native ruby tag support in WebView for SDK 11+, but
fall back on manually aligned spans on earlier versions of Android.
These look better and don't overlap other elements like the
previous CSS table solution does.
Fixes Issue 1648.
Merge pull request #23 from hssm/Issue1648

Use ruby tags and styled spans for furigana instead of CSS tables.
Merge pull request #26 from flerda/v2.1-reviewer-css

Fix CSS in Reviewer for the default font.
Merge pull request #27 from flerda/v2.1-card-debug

Saving the content of the cards.