Complete behat test for inline editing

[NightJar]

#372 as a part of #327 involves adding an inline edit form for elements to allow editing directly in the ElementalArea. This had accompanying end to end tests (behat), one of which proved a little too weak to be included in the merge.

This needs to be fixed with a more robust solution and re-enabled (currently it is commented).

https://github.com/dnadesign/silverstripe-elemental/blob/f25de3e5adf3df474cd7aadef420ab4680313070/tests/Behat/features/element-editor.feature#L25-L37

[robbieaverill]

Fixed in #383, nice one @raissanorth