Simplify filter form display

Currently, the filter form looks like a big monster and there are various issues in the issue queue to add even more (major version compatibility, plurals, even more options for string lookups, etc). So this is going to be an even bigger monster.

Bojhan's video at http://www.screencast.com/t/ZWM2ZDc3 shows nicely that the filter form takes up way too much of the screen space when you encounter the translation page. This is how the filter monster looks now:

So I think we should just limit the filters to the essentials initially and then show more if the user wanted to. I also think the filter button should be made more prominent, and the reset operation could be made prominent in a different way. So I came up with this approach:

The idea is that we only show the project, release and context fields by default and let you expand the form to the full set of fields if you want to. The filter button is enlarged and moved to the top right and the reset button is made a link and is moved to the right bottom. This is basically taking a cue from some core forms where Cancel is just a link, since it skips submitting the form.

If you ask to expand to the full form, it just shows the monster as above, except the filter button and the reset links are at their new place:

And since you then use some of the form elements, the next request comes back with the form hidden again, but all fields where you picked non-default values (plus the project+release+context fields already shown) are visible:

So the idea here is that the default set of fields are always shown, and otherwise all fields are always displayed, which have values.