Merge common settings of build process

[kamilkisiela]

• We had build.js and common.js now it is only one file (common.js)
• development webpack configuration by default
• By defining webpack.entry option in a different way we can easily change name of the output file (like here)
• It's much more logically now and we're not duplicating code
• I also removed deploy settings in .travis.yml

Is there anything to improve or change?

[pbastowski]

Let's use it and see how it behaves and then maybe we'll find some things to improve.

[kamilkisiela]

I've also implemented it in my two other projects so we will test it :)