Add bulk rename support

[AObuchow]

It’d be nice to be able to rename multiple files at once.

3 types of bulk rename that could be available:

• Use the same new name for all files, but add a number at the end to differentiate
• Prefix rename: append the new name to start of old name
• Suffix rename: append the new name to the end of the old name

For now, I imagine this feature would show a dialog, but maybe it could be done inline with a special key command?