Fix inverted arguments for a collision callback

The start and stop callbacks on this line seem to be backwards.
Fixed a couple of errors in the methods definition
Added my own IDE filed in the .gitignore file
Added a destroy method on the Gridster class
Bound leftover callbacks are one of the main causes of memory leaks, let's remove them inside the destroy method
Built new version
Fixed a minor issue when trying to destroy a non existing drag_api
Fix for not removing stylesheets on destroy
Add max_cols setting

Right now the number of columns is calculated by dividing the available
space by the necessary space. I want to have an option to limit the
number of calculated columns, without changing the width of the div my
grid lives in.

In order to limit the number of calculated columns max_cols is set to a
number. To have 'unlimited' columns set the value of max_cols to -1 (as
ids done in the default settings). This provides the arbitrary useful
functionality to set the max number of columns to 0. Any sideeffect
caused by this are mitigated by checking that the max_cols is larger
than the min_cols setting.
Updated Readme added PSA
namespaced events instead of caching callbacks
Pass container width to draggable instance. Relative to 5569caa687
Reverting some changes in commit 6302b98

Check to avoid generation of duplicated stylesheet-tags shouldn't have
been removed from Gridster. It's useful when calling multiple times 
`generate_stylesheet` method once Gridster is initializated. We use it
at ducksboard to generate a TVmode version of the grid with bigger widgets.

Refactored the way stylesheet tags are removed. When created I push them 
to a jQuery collection which is removed when `destroy` method is executed.
Removed `libs` folder from the repo. Install dependencies with bower.
bump up to jQuery 2.0 and start using bower for managing dependencies
Ignore libs folder
Added watch command to Gruntfile config