Show an error for invalid bitcoin.conf settings

[GBKS]

trafficstars

In our user test, one person could not start the app because they had a bitcoin.conf file that was problematic. Instead of the app simply quitting, can we catch the error and show a helpful message?

[GBKS]

#44 seems to be related in that it's about communicating how imported settings are handled.

[yashrajd]

Example.

I like that informative error message if we can generate one for all errors. Not sure about the Continue button if the app cannot start without corrective action.