implement vim's indented paste - adjusting indent to current line

Hi,
This is a first pass at implementing vim's indented paste, `]p`. If this is going in a good direction, I can also add tests and implement  `[p`, which pastes above using the current line's indent.
Two things to note:
*  I've used `vimApi.handleKey` which isn't a standard thing to do. I didn't know if you wanted to instead use `commandDispatcher.processAction` and `commandDispatcher.matchCommand` which starts to implement parts of `handleKey`.
* I set back the unnamed register because this is consistent with vim's behavior: the register doesn't change when using `]p`.