Fix sortable columns styles and dh-field directive bug

Fixed some of the issues left to fix from https://github.com/somawater/deckhand/pull/22:

* Changed the glyphicons for the sort-attributes ones.
* About using a default icon when the column is not sorted: As I suggested in a comment in that previous PR, I don't think this is a good idea, since all the columns are sortable. It will create a lot of visual "noise" since those icons are not adding any value to the user.
* Column wrapping is done because of the width that the browser allocates for each column (since we don't specify any width for different columns so far). However, I moved the icon to the end of the column name so these cases are not that often. Also, the benefit is that the header doesn't "move" when you make an icon appear when sorting by that column.
* Left side alignment fixed
* Fixed the formatting of the columns in the relation tables, there was a bug there.