Website: some improvements to the filters

[siddharth-krishna]

• Add an easy way to select all options in a category
• Add a way to reset all filters across all categories
• Reset filters when moving to a new dashboard
• Use URL query parameters to save filter state so that filtered results can be shared

We had discussed implementing a filter component in the style of Google Flights' filters, but this isn't necessary for now, and we will revisit it if one of our filter categories has too many options to be easily used. However, if while implementing the above features, if you think it'll be less work to re-implement the filter component, then please consider re-implementing it in the Google Flights style. Thanks