Behaviour for heavy pages and hidden elements; code cleanup

[JelleDekker]

Updated behaviour:

• Parts of the page that are not shown (e.g. tab container; closed groupbox) are not loaded until opened by the user. This makes the widget also usable when the MF isn't slow, but the page takes time to process.
• It's now possible to run the widget without a MF. Again for heavy pages
• The return object of the MF is now used. This means you can open pages wich are based on a different entity than the context object.
• Changed CSS to no longer use absolute positioning, for use in groupboxes

Cleanup:

• Added "node_modules" to .gitignore and added package and gulpfile, sow people can now run their own build software
• Removed unused Dojo imports
• Changed parts of the code to be closer to default Mx widget style

[pimvdnoll]

Thanks for your contribution @JelleDekker! @joelvdgraaf will process the pull request