MDL-45054 Conditional availability: HTML structure improvements

1. Changed the 'delete' and 'eye' buttons to use an <a> link
tag so that it works without custom tabindex and shows a correct
mouse cursor. This also reduces the code slightly.

2. Changed the Cancel button on the dialog to use the mdl-align
class which is used in Atto dialogs. This results in the button
being centered, consistent with those dialogs.
Automatically generated installer lang files
Merge branch 'MDL-45054-master' of https://github.com/sammarshallou/moodle
Merge branch 'install_master' of https://git.in.moodle.com/amosbot/moodle-install
Moodle release 2.7rc1