Add typewriter connection information to session.
Add typewriter connection interface to the sheet manager.
Take typewriter connection into account when setting enabled status of editing widgets.
Add a placeholder image for edit icon.
Add edit icon to the list of valid icon names.
Add edit button and corresponding keyboard shortcut.
Filter out autorepeated space bar press in sheet.
Fix signal blocking code.
Merge pull request #218 from kagu/connect_typewriter_toggle

Toggle button for typewriter connection