Add advanced filtering

[joepetrowski]

It would be great if you could add filters in addition to sorting.

Some ideas for filters:

• Commission (less than, greater than, range)
• Amount at stake, absolute or percentage
• Known entity (e.g. you hold a signed message from entity running the validator)
• Last slashed (e.g. no slashes for previous x sessions)

For example, let's say I want to sort by amount at stake, but only for validators with commission less than 30%. First I could filter to only show validators that have less than 30% commission, then I could sort by stake low to high.

[mariopino]

Thanks Joe, very cool ideas! Definitely a must to have them in PolkaStats.