Provide private channel route hints & make private routes sendable

[wbobeirne]

Closes #192

Description

This makes invoice creations include private route hints, and also works around the issue where you were unable to send invoices that relied on private routes due to QueryRoute's inability to take in routing hints, and Joule's running of QueryRoutes before letting a user send to ensure that there is a route and to provide the user fee information before they send.

The latter part of this should be moot as soon as this PR is merged lightningnetwork/lnd#2186 but even then will stay an issue for folks running older node versions for a while. This janky temporary fix of returning placeholder routing info will probably have to sit in for a while until there's a reasonable expectation that most people have upgraded.

I also make a Help component and used it in a couple spots to explain some stuff.

Steps to Test

1. Have a private channel open on your node
2. Generate an invoice with the routing hints checkbox checked
3. Run your invoice through https://lndecode.com/ and confirm the routing_information info is provided and correct
4. Generate an invoice with the routing hints checkbox unchecked
5. Run it through lndecode again, confirm the routing_information info is not provided
6. Attempt to pay the invoice you generated in step 2, confirm that you are able to attempt a send in spite of the fact that QueryRoutes failed
7. Attempt to pay the invoice you generated in step 4, confirm that you are unable to attempt a send since it has no routing information

Screenshots

Invoice form w/ checkbox

Help Tooltip

Invoice prompt with advanced expanded

Display of fees with private routing

[jamaljsr]

Nice! I'll try it out later today 👍

[wbobeirne]

Have had this for a few weeks in testing and haven't had any issues pop up, so I'm just gonna merge this boyo in.