Bug fixes

[Robert-Lebedeu]

CHANGES:

1. Templates:
   • Removed the title inside the change_form template.
   • Commented the _af_handler.destroy() call inside common_js_init because I didn't want to clean up
     every time the add rule button was pressed.
2. Forms:
   • Changed isnull operator from None to 'None' (Before it wasn't working and with 'None' worked
     perfectly).
   • The value field now is not required anymore if you select one of these operators: 'isnull', 'istrue,
     'isfalse' (Also the value field becomes a readonly field, in these cases).
   • I also removed the part that auto-selects the range operator with datetime fields.
     This was creating some issues and I thought it was a useless feature to keep in so I get rid of
     that part.
3. Static:
   • Added try-catch when using Django-Grappelli and JQuery-UI
   • Changed the modify_widget
   • I found some functions that were called twice with out any valid reason, I commented that parts
     and this corrected some bugs (for example: now range operator works properly).
   • I also commented the field_selected(...).first() call because I thought that it didn't make any
     sense to re-initiate the first rule (this problem was forcing you to use always an equal operator as
     your first rule) .
   • I also changed the initialize_select2 function to set the autocomplete only with foreign keys and
     'iexact' operator.

[lorenzomorandini]

This PR actually fixes a lot of JavaScript issues, can it be merged please?

[asfaltboy]

There's a failing test and a few dubious changes, but I'm sure it can be brought to shape. @lorenzomorandini would you care to review & test the code?

[lorenzomorandini]

Ok, I will review it

[coveralls]

Coverage increased (+0.05%) to 95.969% when pulling b902218 on Robert-Lebedeu:develop into 4f1575a on modlinltd:develop.

[lorenzomorandini]

I've been trying this version for a few days and all javascript problems seem to have gone:

• Datetime range works and does not duplicate when adding a new row
• Select2 autocomplete appears only for foreign key fields
• Works without django grappelli too

[asfaltboy]

Update: I'm working on a test suite for JS using selenium, once I am able to anchor all feature and reproduce the issues mentioned here, I this it will reduce the risk when merging this PR.