Allows disabling of timestamps when importing posts

fixes #1696

- this is a temp workaround until full fledged support
is added directly to bookshelfjs
- when importing we use the import json blob’s timestamps
as the value that’s set in the DB 
- added tests for this change
Path, url and subdir cleanup & test

issue #1754

- remove path (it was only used once, and not needed)
- change webroot to subdir
- add unit tests for config.paths
- various other cleanup
- renamed client-side ghostRoot to subdir
- added url helper for client
Merge pull request #1764 from ErisDS/path-cleanup

Path, url and subdir cleanup & test
Static pages do not use dated permalinks

closes #1753
- Pages are registered to '/:slug/' route if posts are using dated permalinks
Correct ARIA role for pagination helper

Fixes https://github.com/TryGhost/Casper/issues/63
Shared folder asset handling

fixes #1659, fixes #1668

- removed relative asset url from css
- added asset helper to client
- updated references to shared assets
- added functional tests
Merge pull request #1772 from markberger/1753-static-page-url

Static pages do not use dated permalinks
Merge pull request #1769 from ErisDS/shared-assets

Shared folder asset handling
Merge pull request #1759 from hswolff/fix-import-updated-at

Allows disabling of timestamps when importing posts