Added customizable content script which is injected into pages

Added a text area where Javascript can be saved which will then be
injected and executed on each page load. Considering adding the option
to select at which point during the tab load the script will be
executed.

The injected script (jira-customizations) is not complete yet as I
realized that access to the jQuery object loaded by Atalassian is not
available inside content scripts. In fact, only the DOM is shared
amongst the page vs. content scripts.

Attempted to add a separate option field for loading an external
Javascript file, but I wasn't able to get the extension to allow it. At
this point, the conclusion is that it can't be done this way
programmatically (only through the use of the "content_scripts" in the
manifest file).

Also started adding additional information inside the popup, though it
is still incomplete.
Injects jQuery before running the user-defined Javascript

Will most likely make the "default value for the Description field" its
own customizable field in the options page since this is a commonly
desired functionality.

Don't forget to add a note in the Options page to indicate that there
will be a certain version of jQuery available for the script and the
option to choose when the script is executed.
Improved (fixed) the default Description value custom code
Added a mediocre, generic-purpose AJAX function

I haven't updated all the AJAX calls to make use of this function just
yet even though it's been tested and is stable.

Noticed an empty object is now being sent to the crxMessage() function
from the popup so no message is ever processed. Don't know when this
started happening but will be looked at next.
Selectable project context, Badge Query based on Favourite Filters

- Added drop down in the popup for selecting the active project context
- The query used for the Icon Badge is now selected from a drop down
field that is populated with all the user's "Favourite Filters" from
JIRA
- Added an option field for defining the default value for the
Descriptions field (before was done manually through the Injected
Script)

- Updated the object property in the template substitution for the
banners
- Started using a config object to house all the default configuration
values
- Added a background image to the options page and cleaned up unused
fields

- Added a gaurd for when attempting to parse undefined JSON data
- Deleting a banner now updates the saved value(s) properly (before they
were only saved "on blur")