Added inline field editing for strings and document removal

Another attempt at the update/delete PR I made a while ago, this time with a different approach. It uses one `updateCollection` field in the main settings object which is used to update the given collection.

* Supports virtual fields
* CSS hides the delete button if you're not hovering on the row
* Non-intrusive as possible in terms of rendering procedure when updateCollection isn't defined (it falls back to regular `getField`)
* Still only works with strings, `null` values update-able as strings
* Delete confirmation using i18n (no translations though)

I might add an 'add document' button in the future, but it gets a little presumptuous. Similar problem with datatypes, but planned to be added in the future also (such as number, boolean and date).

Again, any suggestions for improvements appreciated.
It probably makes sense to decouple the Template.reactiveTable.getField helper to a general helper.