Implement extension-api for accounts

Change-Id: I689f3e17deaa1319e3b731a78efcb83bb97999f9
SideBySide2: Fix no language selection in preference box

Add an option at the start of the list that has no language
selected. This option is used if the type was not detected,
but syntax highlighting was enabled.

Fix the list to pick the active value from CodeMirror rather
than the value returned by the server. This is less confusing
when the dialog opens after the user selects a different mode.

Change-Id: Ica24587ef2773368d2b2eecf4189aaff246f548f
Switch to using new PluginData class

176b801295fbe616689390f8ff4c11b18d1884fc added PluginData class but
missed to switch the code to use the new class.

Change-Id: Iee6665cd4643ad9251e8feadc31894212bd5ee4c
Merge "Implement extension-api for accounts"
Merge "SideBySide2: Fix no language selection in preference box"
Merge "Switch to using new PluginData class"