Change around validator button order, choose default Docker image

[nathanleclaire]

Two things that I think would help users on the validator page:

1. Change button order so "Run Validator" (the most important) is first
2. Select a Docker image by default (I've probably done this wrong on this go round, @SvenDowideit you'll have to tell me the right way to do it)

Signed-off-by: Nathan LeClaire nathan@cryptoworkbench.io

[nathanleclaire]