Add simple replacement for connection manager

[karlb]

The current connection manager is about to be removed (see raiden-network/raiden#4730). It would be good to have a simple replacement in the WebUI.

Using it could look like this:

• User clicks "Join token network"
• UI asks PFS for suggested partners
• User enters amount of tokens to deposit and gets a preview of the recommended channel openings and deposits
• User confirms or cancels

Optional feature:

• User can select which of the suggested partners should be used by (un)checking them in the preview

This will be a lot simpler and more transparent then the current process of joining a TN. As a downside, there won't be a mechanism to ensure deposits in both directions. This is ok if the user only wants to pay, but it will be a problem when receiving payments.

[sashseurat]

@manuelwedler & @karlb
After discussing this with Manuel, here is a static design draft for the dialog concept:
https://www.figma.com/file/1GEZifHDJCxEN4F8UU7PVL/Quick-Connect-Redesign?node-id=0%3A1

• Each suggested connection can lead to its network graph visualizing the connection for the user (external link to explorer)
• The ? icon nest to total deposit can lead to/show info on this logic and what is expected of user
• Slider for each connection is moved by user, displaying the deposit sum in the adjacent input field - user can also type in input field instead of dragging slider
• The default is the total amount divided equally between suggested connections

[karlb]

Looks good!

I suggest that when a user draws the slider fully to the left or enters zero, that no channel gets created (instead of creating a channel and not depositing any funds).

[manuelwedler]

Perfect, that's what I had in mind. We can make the partner appear transparent or grey in that case, so it is clear that no channel will be created.