Introduce GPG operations

Add methods for cryptographic authentication of Cask packages with
the GPG software suite.

Homebrew Cask invokes the system-standard `gpg` binary to import
keys to the GPG keychain, download signatures to versioned metadata
folders, and verify packages. Homebrew Cask aborts if any step fails.

GPG verification is not currently invoked during the audit or
installation processes, and is intentionally left undocumented.

Example usage:
    gpg = Cask::GpgCheck.new(cask)
    gpg.verify(package_archive_path) if gpg.available
revise accessibility methods in postflight miniDSL

* rename `remove_accessibility_access` to `disable_accessibility_access`
  to match corresponding method `enable_accessibility_access`
* move `TCC.db` and `.AccessibilityAPIEnabled` paths to `Cask::Locations`
* remove unneeded backslash from `TCC.db` path
* use full paths to `touch` and `sqlite3` utilities
* use `@command.run` instead of `system_command` which is intended as an
  external interface
* reverse conditional so enable/disable logic is consistent
* `sudo` is needed when creating `.AccessibilityAPIEnabled`
* instead of silent fail, warn that access cannot be safely disabled on
  Mountain Lion and earlier (it could, but might affect other apps)
* quoting/whitespace
revise plist methods in postflight mini-DSL

* accept index argument to `info_plist` in case of multiple `app`
  artifacts, defaulting to first
* return `Pathname` object from `info_plist`
* use `@command.run` instead of `system_command` which is intended
  as an external interface
* quoting
revise move_to_app method in postflight mini-DSL

* use `@command.run` instead of `system_command` which is intended
  as an external interface
* quoting
virtualbox: change license to GPL

From https://www.virtualbox.org/wiki/Downloads: "The binaries are
released under the terms of the GPL version 2."
Merge pull request #7717 from L2G/virtualbox-license

virtualbox: change license to GPL
Change ownCloud license to GPL

See: https://github.com/owncloud/mirall/blob/master/COPYING
Update ownCloud to 1.7.0.1490
Merge pull request #7719 from riyad/update-owncloud-to-1.7.0.1490

Update ownCloud to 1.7.0.1490
Merge pull request #7718 from riyad/fix-owncloud-license

Change ownCloud license to GPL
Change iTerm2 license to GPL

See: http://iterm2.com/ or https://github.com/gnachman/iTerm2/blob/master/README.license
Merge pull request #7720 from riyad/fix-iterm2-license

Change iTerm2 license to GPL
Add PSequel.app latest
Merge pull request #6184 from ndr-qef/gpg

Introduce GPG operations
Merge pull request #7721 from houshuang/psequel

Add PSequel.app latest
Fix maintenance links for 10.8-10
Add Yosemite and legacy downloads for deeper
Merge pull request #7727 from jawshooah/fix-maintenance-links

Fix Maintenance links for 10.8-10
Merge pull request #7728 from jawshooah/deeper-legacy-links

Add Yosemite and legacy urls for Deeper
Upgrade EasySIMBL to v1.7.1

- Upgrade EasySIMBL to v1.7.1
- Remove unnecessary trailing slash from GitHub-hosted homepage url
- Change license to GPL
  (https://github.com/norio-nomura/EasySIMBL#license)
- Add zap stanza