Add link to zip download

Adding the complementary part to mkly's changes, making it more friendly for newcomers to know how to get the latest development build without having to know how to navigate GitHub.
Remove hardocded textarea width from form block output
Added file description to data returned by the files/get_data tool
set fixed height in slideshow block
determine max height of slideshow images
constant to hide concrete5 version number

as mentioned here http://www.concrete5.org/community/forums/chat/visible-version-number-in-source-code/
don't output unnecessary jquery UI in form block

Take 2 (see https://github.com/concrete5/concrete5/pull/672 for prior discussion).
Also outputs CSS to header (not footer) if needed.
Fix blocktype sort mismatches

Removes gaps in the btDisplayOrder sequence whenever a blocktype is deleted. This prevents future problems when sorting the remaining blocktypes in the dashboard list.
Fix: Login loop with cookies disabled

When trying to login with cookies disabled no error message is shown to
the user. Some 'corporate' networks have this setup by default, I have
experienced it recently with Concrete & a client.

The patch below modifies the login controller to throw an exception on
cookies being disabled.
Close two not closed <div>
Remove extra </div>
Remove extra </div>
Move misplaced start of form
Remove extra </div>
Remove extra </div>
Add missing </div>
Add missing </strong> and removed extra </form>
add fileset file addition and removal events

added two events:
on_file_added_to_set($file_id, $file_set_id)
on_file_removed_from_set($file_id, $file_set_id)

it seems when using the UI and updating the sets a file is in
all associations are removed and then re-added based on the checkboxes
which causes the on_file_added_to_set event to be triggered multiple
times for sets the file is already in. However, when called
programatically these events will be fired as expected
input check in file download statistic

it's not in issue in the core but if someone uses the method
getDownloadStatistics and allows the user to specify the limit,
we're opening a security hole.
Refactor getBlocks, a cleaner pull

Single clean re-work of
https://github.com/concrete5/concrete5/pull/842