Makes plugin sendTransaction work with non-vm providers, adds tests

[bmcd]

Even though #1265 fixed silentRunTx to allow non-VM transactions, I found some issues while trying to use udapp.sendTransaction from a plugin:

• The tx would go through when using Web3 Provider, but in the final callback there were some VM-specific result values that were being used, causing it to throw an error.
• This error wasn't being sent to the reject() function in the promise, so the plugin just got undefined and didn't know what the error was.
• The result object that the callback for silentRunTx() has 3 different forms depending on the environment and transaction type, but only the VM type was handled.

This PR adds:

• a try/catch to send any errors to reject().
• a helper method that converts the different possible result types into the expected RemixTx object.
• UniveralDapp didn't have any test coverage, so I just made tests for the helper method it calls, with example result objects that I got during testing.

Please let me know if you want me to change anything. Thanks!

[Aniket-Engg]

Thanks for this @bmcd87 . Almost everything looks fine.