new splash screen

why:
- the current splash-screen has no referring to official images on https://en.bitcoin.it/wiki/Promotional_graphics
- the current splash screen only exists in a low res jpg
- current splash screen looks dark and "hackish"
- new splash screen should generate positive, "trust-emotions".
- new splash screen gives the user infos about the running client.
- new splash screen can handle long messages (in a lot of languages the text is cropped in current release)

- example: https://dl.dropbox.com/u/7383846/new_bitcoin_splash.png
- new size (x2) 400x312
- contains textual information about the client
- a imagemagick script *could* place the text dynamically on the splash.png (like the about gui screen)

Signed-off-by: Jonas Schnelli <jonas.schnelli@include7.ch>