Use desktop login/account creation form in alpha

Changes for mobile:
* Hide labels and use placeholders for inputs (Fixes bug 68758)
* Avoid duplicate messages by using desktop version (bug 71771)
* Fixes "Input blue indicators look strange when rounded corners are applied to mediawiki ui inputs" (bug 69724)

Other changes:
* Use variables for warning, error messages on login form
* Remove error styling introduced in I6b5b98414ceeac6b467b1b7ef29a4cfd8a81a149 now
it is only used on nearby page. Move to nearby and use standard colors
* Remove generic textarea, input field styling now we are using mediawiki ui

Bug: 68758
Bug: 71771
Bug: 69724
Change-Id: I8f89bdaf3dc7fde104f199554b18486c30580910
Merge "Use desktop login/account creation form in alpha"