Now that we support webview fallback packages - packages that should be
enabled if and only if no other webview packages are available - we need
to ensure that the Settings UI consistently shows that these packages
cannot be enabled or disabled (e.g. the 'Enable' and 'Disable' buttons
for enabling/disabling them are greyed out).
Also, remove the Dialog that lets a user enable a disabled webview
package from the webview implementation Dev Setting. Instead show a
Toast if the user has chosen an invalid package.
Bug: 26375524, 26375860
Change-Id: I949083d3f7c83cd2e049dd2c5c15ec5ab880fe07
Instead move the functionality back into overflow menu as show/hide
system apps. Also move the reset app preferences from advanced to
the overflow menu.
Bug: 20210160
Change-Id: Ied573e1f7dfc438b06642ee2af8f11868130ba3b
