Ignore config files

Remove config files from .gitignore.

Ignore config files using 'update-index --assume-unchanged':

git update-index --assume-unchanged build.properties
git update-index --assume-unchanged src/database.properties

(See
https://help.github.com/articles/ignoring-files#ignoring-versioned-files
)
Merge pull request #53 from jembi/ignore_config_files

Ignore config files