Message

Summary:
* styles messages view
	* because there was no data in the database, this hardcodes in the message list items html & jquery for quick testing (card , card actions and card panel elements).
		* this can be extracted into 'MessageListItem.html` once data is present, for correct integration.

* further modularizes Sass by creating & @importing partials directory
* styles dropdown buttons across app
* adds map placeholder image

Refs T135

Test Plan:
Look at 'Messages' view
* click 'Lamu' (location), 'Expand' & 'Reply' to see styles and test functionality.
* resize browser for responsive view, especially card actions dropdown button.

Reviewers: eyedol, dkobia, rjmackay, shadowhand

Reviewed By: rjmackay, shadowhand

Subscribers: digitalafrican, seth

Maniphest Tasks: T135

Differential Revision: https://phabricator.ushahidi.com/D26