Caching of the JS bug field definitions
Remove BayotBase.fields() webservice method

Adapted Javascript Bug object to use the cached field definitions
instead and removed the webservice method
Improve field definitions cache file handling
Set also file permissions under field defs cache dir
Make opsys and platform mandatory, if defaults not set
Add is_default to select field value definitions
Add multi value support to user autocomplete field
Merge branch 'master' into devel
Add keyword autocomplete jQuery widget
Made JS Rpc object methods chainable
Field definition improvements

Added visibility and value restrictions to status, resolution and
product specific fields.
Field visibility controls in JS
Refactoring and various fixes in Bug JS object

* All publich methods which require field accept eiher field name or
  field description object
* Alerts from Bug objects can be disabled (probably will be removed
  completely at some point)
* Bug.fd() class method removed and replaced with field() object method
Fix default value handling