Post Create View

Summary:
### post create

* adds post create html & sass

* adds `postCreate` controller

* adds mock data to 'post'

* adds test data to forms

* separates post detail and post create

* adds block grid mixin
  * used in "choose form"

### post create - basic form

* markup and styles

* adds translations to `en.json`

* adds to `post-create-controller.js`
  * `isLinks` function
  * leaflet extends
  * add` and `remove` links function

* adds links attributes in `attributes.json`

* basic form to `forms.json`

### post create - attributes

* added placeholders to form attributes

* removed redundant labels

* reduces specificity on leaflet map for global z-index.

### post create - buttons

* clarified the back button

* added border-radius to `<a>` buttons

Fixes T1135

Test Plan:
This is the first pass at "Post Create". @brandonrosage, @sebm90 and @seth are considering a custom dropdown on "Create" for picking forms (similar to user info dropdown). For now a form picker view is available, with a back button on form to return to form picker.

* in top nav bar, click create
* confirm redirect to form picker view and check responsive layout
* click "Basic Form"
* check form attributes, UI and responsive layout

TODO:
choose a date picker method
add a default selected "choose one" option in `<select>`
fix the links UX
  * trash can icon removes last item in array. Fix so the correct row is deleted.

Reviewers: rjmackay, brandonrosage, shadowhand

Reviewed By: shadowhand

Subscribers: brandonrosage, spaudanjo, sebm90, digitalafrican, srutto, dkobia

Maniphest Tasks: T1135

Differential Revision: https://phabricator.ushahidi.com/D540