Queries the homeserver for PSTN protocol support, and if found,
the add-room button on the DM rooms list section opens a context
menu instead with a 'dial pad' option as well as the current 'start chat'
dialog. Entering a number into this and pressing dial performs
a thirdparty user query for the given string and starts a DM with that
user.
This removes all images we no longer reference in the app. This should be safe,
as Webpack only adds images to the build output if they are referenced.
David Baker