Surge++ Error Reporting could be better than stdout

[baconpaul]

Right now Surge++ LayoutEngine has a LayoutLog::error() which adds things to stdout

We probably want to do something smarter than this; like push the collection of errors to the user in a popup at the end of a layout cycle and the end of a parse.

So make the little error() class keep a list of messages and in a couple of spots in SurgeGUIEditor (probably the LayoutEngine constructor and parser; and the openOrRecretateEditor) ask if there was an error and show it with UserInteractions::promptError() (for now).

[baconpaul]

Re-tooling the S++ plan so closing these issues.