This commit adds a label in RoomSettingsPage to indicate whether encryption is enabled in the room. It also adds a button to enable encryption for an unencrypted room.

Type: add

Closes https://iron.lily-is.land/T68

Verify that unit tests pass.

Open the settings page of an encrypted room. It should show the room is encrypted an has no "Enable encryption" button.

Open the settings page of an unencrypted room. It should show the room is not encrypted and has an "Enable encryption" button. Clicking on it should open a popup asking you whether you want to do it. When you click Cancel, nothing should happen. When you click Ok, it should proceed to send a state event.
If you have permission to send an m.room.encryption state event, clicking on it should results in the room being encrypted, and any new messages you send should be encrypted. If you do not have such permission, it should display an error.