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
Fixed admin 404 page broken image refrence
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
CSS and layout fixes for image uploader

closes #1673
- dropzone icon doesn't appear when filestorage is false
- proper cursor and no selection on icon
- cleaned up some sass
Merge pull request #1674 from ErisDS/css-fixes

CSS and layout fixes for image uploader
Update default fixture to give clearer direction

issue #1561
- altered perspective of the intro paragraph to reading from the blog
instead of from the content page
- also added copy directing the user to /ghost/ to sign in and edit the
post
- this should give the Markdown lessons better context so new users
aren't confused as to what 'the left hand panel of Ghost' is