Add dropdown filter to show rooms, languages, session types. Ensure it works in mobile view.

[mariobehling]

The previous eventyay version had different kinds of filters. Implement filters for the following as well on
a) the Schedule page and
b) the Sessions page.
Ensure this also works on mobile views. Compare to https://eventyay.com/e/55d2a466/schedule

1. Rename current "Filter" to "Tracks" and make it into a dropdown list.

2. Add more dropdown filters as follows:

• Rooms
• Languages
• Session types

3. Also add an option to clear the filters

4. Ensure it works on mobile similarly to the previous version.

[mariobehling]

The dropdown menu works, but there is an issue with the types filter @lcduong