Add ability to define multiple slack nodes in Kapacitor

[russorat]

connect influxdata/kapacitor#1696

• ensure that the latest changes hasn't broken the existing slack config in chronograf
• add the ability to configure multiple slack integrations in chronograf

[jaredscheib]

Blocked until all of the TypeScript conversion work that @ischolten is doing for #2786 is separated out as its own PR, submitted, and merged into master.

[alexpaxton]

If the user configures the slack endpoint, a second slack endpoint appears. If the user configures the second endpoint a third appears. This pattern allows for as many slack configs as necessary with as little changes to UI as possible

[russorat]

how do the tabs look when they scroll? Also, we have a PagerDuty v2 and OpsGenie v2, will users think this is Slack v2?

[alexpaxton]

I'm working on a better design

[alexpaxton]

Changes:

• Configure --> Configured
• Green checkmarks are no longer necessary, as the list only shows configured endpoints
• Add an Endpoint dropdown shows full list of endpoints that can be configured
• Selecting an endpoint from the dropdown adds it as a tab in the list
• Some can be added multiple times

• Dropdown in Alert Rule Builder uses li.dropdown-headers to delineate more clearly the two sections in the menu
• If there are multiple Slack endpoints (for example) then Slack shows up twice in the menu

[alexpaxton]

Spent some more time experimenting with the design. Considering that we may redesign much of the kapacitor config UI in the future it is more strategic to do something really simple for now. Essentially, users will be able to create multiple "configs" within the same tab for an endpoint. If there are multiple configurations each one requires a nickname.

If multiple configurations exist, each has a Delete button to remove it entirely. If there is only a single configuration there is no Delete button

Nicknames are exposed in this dropdown:

Even though multiple configurations appear in the same tab, they should be treated as individual configurations with their own saving/testing functionality

[russorat]

looks good!

[russorat]

• parse error when trying to save a second slack node without filling in an id. error should be shown to the user.
• alert builder, when switching to a different slack node, does not update the script (see below)