WIP #86 HTML for landing page

The following things have been updated:

+ The beta invites landing page has been updated with the discussed styles
+ A new structure for stylesheets was set, due to lack thereof
+ Font and image files were introduced (Might be worthwhile to look at a web font library)
+ The flash messages received minor styling
+ All the registration/login forms received similar style updates
+ The nav and header layouts were merged to avoid repetition
+ Conversation styles were adjusted
+ Since all the layouts were unstyled, a few classes were added/removed to allow for new styles and consistency


[WIP 86](https://assemblymade.com/support-foo/wips/86)