backbonejs model conflict with connect-slashes

close #1648
- backbonejs model doesn't include tailing slash by default
- connect-slashes returns 301 for GET without tailing slash
- overwrote backbone model url method to include tailing slash
Merge pull request #1648 from KingKarl85/api-slashes

backbonejs model conflict with connect-slashes
Change message when unsupported node version is used

no issue
- changed ‚the latest‘ to ‚a supported‘

Reason: the user is asked to update to the **latest** version of
node.js when v0.11.* is installed but v0.10.* is required
Bug fixes for partial views

closes #1203
- Update express-hbs module to the new version (0.5.2)
- Use two instance of hbs one for the theme and an other for the admin
- Template helpers are register as partial view
- Partial views of the theme are reload when the theme changed

Remove clear partial cache in handlebars

This code will be move in `express-hbs`.
This doesn't cause a problem to remove this line but it is not clean.

Remove unused hbs instance

Resolve conflict
Merge pull request #1660 from sebgie/version-number

Change message when unsupported node version is used
Merge pull request #1606 from Gotvitch/issue1203

Bug fixes for partial views
Standardize file path access throughout ghost

resolves #1390

update all string based references to file paths
to use the ./core/server/config/paths file
so that it is the single source of truth