Fix pathless transactions crashing tx list

[wbobeirne]

Closes #206

Description

Fixes some payments (I think only quite old ones) from crashing the transactions tab. This happened due to them coming back with undefined paths. In total, this PR does the following:

• Defaults the path array to [] if undefined
• Improves the display of pathless payments
• Improves the Identicon component by having it display a (?) when the pubkey is falsy

Steps to Test

1. Get a pathless payment, or alter the code so that you can forcefully induce one
2. Load the transactions tab, confirm it doesn't crash
3. Open a pathless transaction, confirm it displays correctly

Screenshots

List view

Detail view

[wbobeirne]

Confirmed working here: #206 (comment)

Merging in!