Re-factored tag map constraints to allow custom ui messages for status-based constraints

- Changed constraint messages in VLE to render in a jQuery dialog (which can be themed) instead of browser alert
- Added default messages for 'isVisitable', 'isVisited', and 'isCompleted' status type constraints
Added tag map constraint messages for EpigameNode

- Step type locales now load synchronously so that step i18n is available to node constructor
Deprecated 'MustCompleteXBeforeConstraint' and 'MustVisitXBeforeConstraint'

- WISE now creates XMustHaveStatusYConstraint instances instead (using 'isCompleted' and 'isVisited' status types set to 'true')