Add a donation pool for Groestl
Merge branch 'feature/add-donation-pools' into develop

Conflicts:
	MultiMiner.Engine/Helpers/DonationPools.cs
Update version info
Cache network difficulty based on pool URI rather than coin symbol
Merge branch 'bug/questionable-diff-cached' into develop

Conflicts:
	MultiMiner.Win/Forms/MinerForm.cs
Update version info