Bitcoin-Qt: give testnet a unique IPC message queue name

- this prevents an interference with the IPC message queue (which is used
  for URI processing) when running a testnet and mainnet instance in
  parallel
- to check for testnet, I had to raise the ParseParameters() call in
  main() to the topmost position
update noui_ThreadSafeMessageBox function to use strCaption

- ensure we use strCaption for printf and fprintf, as before it could
  happen to have an error message in the debug.log, which had no "Error"
  (or whatever) in front
Bitcoin-Qt: add a Signature label on sign message page
Bitcoin-Qt: fix small stylesheet glitch in overviewpage.ui
Merge pull request #2143 from Diapolo/ThreadSafeMessageBox_caption

update ThreadSafeMessageBox function to use strCaption
Merge pull request #2147 from Diapolo/mq_name_testnet

Bitcoin-Qt: give testnet a unique IPC message queue name
Merge pull request #2151 from Diapolo/signmessage

Bitcoin-Qt: add a Signature label on sign message page
Merge pull request #2153 from Diapolo/overviewpage

Bitcoin-Qt: fix small stylesheet glitch in overviewpage.ui