Made admin panel tables sortable and filterable

[sheldor1510]

• Added functionality for admins to sort tables in any order (asc or desc) and filter the rows by a specific value
• All parameters for sorting and filtering are stored as GET vars in the URL (for bookmarking specific links)
• Make admin panel tables sortable and filterable #70

[hakasapl]

Finally got a chance to test this. This works well as is, but I have a some front-end changes:

1. Change the cursor to a pointer when hovering the sort or filter buttons using css: cursor: pointer
2. The filter textboxes don't fully align with the table headers. I would suggest using javascript to determine the current length of the column in question, then dynamically set the width and position of the text box depending on that. Keep in mind the column widths can change depending on the size of the browser, that's why javascript is needed.

I would also like to be able to filter by multiple fields at the same time, but that doesn't have to be in this PR.

Good stuff, thank you!

[hakasapl]

Nice work!