- added bootstrap3 template pack
- updated bootstrap.py module to look at TEMPLATE_PACK instead of directly ref 'bootstrap'
- collapsed appended_text, prepended_text, and
appended_preprended_text into one class and template, the three were almost identical
- added input_size to prepend append handler
- corrected css classnames control-group > form-group, help-inline > help-block, alert-error > alert-danger
- added css class form-control to CrispyFormNode if bootstrap3
- updated crispy_addon tag to comply with the revamped prepend_append handling
- updated test assertions to cooperate with bootstrap 3