Import NonLockingScrollView from AOSP Email client.

As contained in current AOSP master:
https://android.googlesource.com/platform/packages/apps/Email/+/b3c37a31ccffe137cc9b1c1068bb99d3d00a2ee4
Switch to using NonLockingScrollView

This implements the AOSP Email solution for incorporating
a Webview inside a ScrollView, while still being able to
scroll diagonally.

This replaces the functionality of TitleBarWebView (which
is now removed).
Revert auto-scroll changes that are no longer needed.

Revert "Only Jelly Bean seems to have the auto-scroll issue"

This reverts commit a3802a7a8eece86f31070868f9ba7c9c7b23f92e.

Revert "Hack around WebView's initial auto-scrolling past the message header"

This reverts commit 8dcc769c50ab4cfb7c5b8f8f9b5bed3fd28801c2.

Conflicts:

	src/com/fsck/k9/view/MessageWebView.java
Import RigidWebView from AOSP Email client.

Also import prerequisite classes.

As contained in current master:
https://android.googlesource.com/platform/packages/apps/Email/+/b3c37a31ccffe137cc9b1c1068bb99d3d00a2ee4
Move AOSP files.

Patch RigidWebView for K9.
MessageWebView would need to extend RigidWebView.
NonLockingScrollview fixes.

Implement methods missing in API 7

Fix coordinate reference frame mismatch.  Touch events are
relative to the view display, whereas view children are relative
to the view.
Use non-deprecated constants
LinearLayout fill_parent

(Don't think it really matters.)
Fix missing 'download remainder' button.
Merge pull request #415 from zjw/non_locking_scroll_view_rebased

Kit Kat UI issue