Nav bar search functionality

[yuchendong13]

Currently, we have implemented the search bar in the navbar UI but have not associated any functionalities with it. Furthermore, the filter button is disassociated with the search bar.

Actionable:

• Link nav bar search bar to the posts and communities page for search queries
• Add posts/communities filtering as a dropdown to the filter button currently next to the search bar
• Move filter button closer to the search bar for more intuitiveness
• Add onChange searching and add a onClick event to the search icon