Abstracted helper functions to separate file.

Not sure how abstract it should be.
Array helpers: select and merge.

Merge is a lot better now, but sometimes the filter call doesn’t leaves
some incorrect values. That’s why I’m calling it twice for now. FIXME!
Fixed updating x- and y-domain
Fixed charts to watch only the y-domain.

Not the x-domain which never changes.
Moved merge function to helpers.js
Enabling map again.
Minor changes.