Java.g4 formatting  - tabs & alignment

Signed the contributors.txt file. 

Changed all tabs to spaces for consistency. The pattern seems to be as though 4 character tabs were used, but tabs were used some times and spaces other times, so I changed to all spaces, no tabs. (File listings on github seem to use 8 char tabs.)

Also aligned some text.

Java.g4 was tested with files from several Java7 books and with the java source from jdk1.7.0_25.

I have no idea why my pulls to sync with the antlr/grammars-v4 master are listed here but the file changes are right.