Throw ve.Error instead of string literals
Throw ve.Error instead of string literals

Throwing strings is bad because it doesn't include a lot of important
information that an error object does, such as a stack trace or where
the error was actually thrown from.

ve.Error inherits directly from Error. In the future we may create
more specific subclasses and/or do custom stuff.

Some interesting reading on the subject:
* http://www.devthought.com/2011/12/22/a-string-is-not-an-error/

Change-Id: Ib7c568a1dcb98abac44c6c146e84dde5315b2826

wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui,wikimedia/oojs-ui