Some tiny improvements

Major changes:
* Saves a few block state creations by comparing the block material instead of creating the block state for each clicked block (inside the interact event handling).
* cancles the interact event if the sign is going to be edited: prevents placing of blocks against the sign.

Tiny changes:
* Saves parsing the integer from the string twice inside the command.
* Added gitignore file (mainly for my forked repository, otheriwse it would have committed all those unneeded files)