Change filter search to a textarea, to avoid hotkey conflicts

[paulroub]

Fixes #143

The SE keyboard shortcuts ignore <textarea> elements, so using that in place of the <input> avoids the issue.

[gunr2171]

Can confirm this fix works. I can type all characters in the filter text box and shortcut keys work when the box does not have focus.

[machavity]

Currently conflicts with the repo. If you can resubmit with an updated version will approve it.