Updated main nav, tidied card styling, cleaned up modal for styling

Updated Main Nav
   - now includes all nav items and dropdowns.
   - added a settings cog for log in and out and perhaps to switch languages in future

Tidied card styling 
   - improved look and layout to cards on the home page river
   - reduced size of fonts and added background for card header to separate the elements
   - added a cleaner and clear add button on the top of the river (will move a smaller version of this to the profile page

Cleaned up modal styling
   - Minimised the size of the comments input to reduce eliminate the need to scroll
   - Removed some of the excess styling coming through the add doc and disasters widget