feat(ui): add TICKscripts page

[sranka]

This PR adds a UI page that contains only TICKscripts.

• there is a new TICKscripts menu item in the navigation sidebar, it goes a new TICKscripts page
  
• the page shows a list of TICKscripts of a selected kapacitor, the list the same as on the existing Alert Rules page, it can be filtered by alert rule name
  
• at most 100 kapacitor rules are fetched from kapacitor when the page is initially opened, the user is informed if the list is truncated and can proceed to load all items. This filter-less operation is quite quick since it loads just 100 rules from kapacitor.
• when a filter is supplied, all rules must be fetched from kapacitor (which takes much longer time that fetching 100) in order to filter by alert rule name
• the list of TICKscripts is paginated when more than 100 items are shown, changing a page take the user to the top of the list
  
• unlike the existing Alert Rules page, the TICKscripts page shows just TICKscripts. It is then much quicker because chronograf does not need to parse every TICKscript to see if it is a rule that is compatible with Alert Rule Builder. More details are explained in #5460
• the edit/create TICKscript page is opened with l=t query parameter, so that its Exit returns back to the TICKscripts page (would be Alert Rules otherwise).

This PR is a part of a solution to #5460.

• CHANGELOG.md updated with a link to the PR (not the Issue)
• Well-formatted commit messages
• Rebased/mergeable
• Tests pass