Initial attempt at blockwise repetition command (aka `.`, aka dot)
Blockwise refactorings:

- Got rid of TextBlockContentBuilderRegister.
- Added blockwise yank operation and command.
- Fixed issue with yanking past the end of line.
- Fixed typo.
Remeber selection in BlockwiseYankCommand for `gv`.
Better edge cases handling in blockwise operations.
Merge pull request #248 from igrekster/blockwise-repeat

Initial attempt at blockwise repetition command (aka `.`, aka dot)