Enable VisualEditor for all users on test2wiki, experimental also

Bug: 51884

Change-Id: I67d898c1e5add1388a3a4cfd3ab1dac19f66a2bc
Hide the new 'visualeditor-betatempdisable' preference if in alpha

Change-Id: I57cb738061068d4cc8d068bbf0c90b0ae9e84c28
Merge "Enable VisualEditor for all users on test2wiki, experimental also"
Merge "Hide the new 'visualeditor-betatempdisable' preference if in alpha"