Tweak style on "Create Another Task" button

Summary:
Not totally sure I'm in love with this but I think it's somewhat non-terrible,
despite the lack of lens flare.

Also made "Cancel" take you back to the task if you got to "Create" from "Create
Another Task".

Test Plan:

• Style:

https://secure.phabricator.com/file/view/PHID-FILE-ad37d3c1f3b2c7a7a7d1/

• Hit "Cancel" from "Create Another", got sent back to task.
• Hit "Cancel" from normal create, got sent back to list.
• Tried to save an invalid task after making changes to CC/Projects, changes

were preserved.

Reviewed By: codeblock
Reviewers: hunterbridges, jungejason, tuomaspelkonen, aran, codeblock
CC: aran, epriestley, codeblock
Differential Revision: 736