Fix discover to panels preserve extra filters on filter-bar

[jesusgn90]

Hello team, this pull request fix a little non-desired behaviour whenever a user has a custom non-pinned filter on any overview/agent tab and goes to Discover sub tab then come back to Panels sub tab.

The trick here was to add a boolean variable to check if I'm on the same tab but come from Discover or if indeed I'm new for this tab. If localChange is true it means we are on that situation, otherwise it'll be false.

Finally, and using localChange, we can decide what to do on the right way:

$state.filters = localChange ? $state.filters : [];

Best regards,
Jesús

[havidarou]

LGTM!