Add a base class (or mixin) for working with forms

[Randy Syring]

Example: https://github.com/level12/gb-h2r/blob/c78156c1b5891f6ee49b42b489e747ffa6a1de0e/how2recycle/libs/views.py#L175

Presumably, they created that as a mixin instead of a base class for the flexibility. We might want to provide both, with the base class using the mixin. If we do that, maybe we should do the same for the GridBase?

[Randy Syring]

@guruofgentoo you up for changing the FormMixin a bit with some of the changes I made here: https://github.com/level12/brecham-marshal/blob/master/marsh/libs/views.py#L37

• A form_create() makes it easier to override just that functionality, which I found helpful in Marshal.
• rename the "on" methods so they start with "form_" so that all form mixin functionality that isn't get/post have the same prefix.
• use "page_title" vs "title" to be more specific?

[Matt Lewellyn]

Yep, I'll get that done here shortly.