translations update 2013-04-08

- updates for bitcoinstrings.cpp and bitcoin_en.ts
- changes help text for -rpcthreads to match -par
- fix a small glitch with -par to be "-par=<n>"
overhaul of the testnet icon (green color) and the toolbar icons

- redefined the green color
- created new toolbar icons
- updated the assets-attribution.txt

Signed-off-by: Jonas Schnelli <jonas.schnelli@include7.ch>
better quality windows .ICO icon file

- icon quality of the win icon of <256px resolutions are now much better

Signed-off-by: Jonas Schnelli <jonas.schnelli@include7.ch>
Merge pull request #2487 from Diapolo/translations

translations update 2013-04-08
Merge remote-tracking branch 'jonasschnelli/new_icons' (#2497)

Conflicts:
	doc/assets-attribution.txt