Rename "pastebin" database to "paste"

Summary:
See D20650. Long ago, this got added as "pastebin", but that's the name of another product/company, not a generic term for paste storage.

Rename the database to phabricator_paste.

(An alternate version of this patch would rename phabricator_search to phabricator_bing, phabricator_countdown to phabricator_spacex, phabricator_pholio to phabricator_adobe_photoshop, etc.)

Test Plan:

• Grepped for pastebin, now only found references in old patches.
• Applied patches.
• Browsed around Paste in the UI without encountering issues.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Differential Revision: https://secure.phabricator.com/D20661