Several fixes regarding gitignore.

[deep110]

• Remove absolute path of Config.java. Also add a sample Config file so that anyone can build the project using their own key values.
• Add .idea files to it

[hareshkh]

@deep110 : For adding a default Config.java and then make git not track it every user has to run
git update-index --assume-unchanged <filename> after clone. So if something is expected after clone and before first build it is better to add a Config.java rather than running this command.