added Multipart Entity type

a special type of entity class that can be made of dissimilar ‘parts’
specified by an associative array of part names and the classes they
should be made from.
converted Thumbnail helper to Multipart entity
added create() to entitycollection

this will allow for create() calls on a collection (most default helper
objects) which will spawn a more useful one-off entity instead of
always storing each entity made thru add()
jumbotron create accepts 1 or 2 string shortcuts
added BootstrapFrameworkException

for use when the libraries have been called incorrectly. e.g. when the
function requires a certain pattern and didn’t get it.
buttonhelper fixes

moved ‘id’ and ‘link’ into htmlAttributes now that framework has more
dynamic support