Integrate postinstall grunt task into build one

[yuijim]

This is related to #48 . I did a quick fix for that one, but as the result of it the grunt postinstall task is run twice when using yeoman generator. In theory running this task could be removed from package.json now to prevent that, but then if someone clones existing project he would have to remember about running it manually, after bower install & npm install, but before grunt build. This is far from ideal.

On the other hand, even now when you join the project you need to know and remember about executing those commands in proper order, since postinstall task is fired after npm install, but it needs to have packages from bower already in place. It may lead to some frustration before one realizes what is happening (it did for me ;)).

So I would like to suggest removing postinstall task invocation from both yeoman & packages.json and instead add that as a first task in build & default tasks. It is a short one, so it won't affect performance and at the same time it will allow to avoid above problems.

[luboskmetko]

You are right about the order of bower and npm install, Ula. Even that's documented in Collaborating section, it's not ideal. So if moving this to the build tasks solves this, then great.

[luboskmetko]

I'm removing the Workflow change label from this issue so we could implement this right away and not wait 2 weeks. This doesn't affect the workflow in such way that people have to learn new stuff or get used to it.