Update config.theme() after every settings edit

fixes #1645

- removes server.get('ghost root') as it is only an alias
to config.paths().path, and adds unnecessary indirection
- removes config.theme().path as its just an alias to
config.paths().path, updated all relevant references
- update config.theme.update to only require the api/settings object,
and no longer need the config object
- modify api/settings.edit to call config.theme.update so that
the themeObject is ready for next rendering of template
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
Fixed admin 404 page broken image refrence
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
Merge pull request #1651 from hswolff/issue-1645

Update config.theme() after every settings edit
Merge pull request #1662 from PaulAdamDavis/master

Fixed admin 404 page broken image refrence