clipbrd: Some small addition and fixes

The patch makes the following:

• Change maximum clipboard format name length to 79
• Change SetDIBitsToDeviceFromClipboard to correctly use the requested format instead of always using CF_DIBV5
• Enable/Disable the menu point "Save as..." dynamically
• Remove unneeded import libraries
• Add WS_EX_ACCEPTFILES window style and handle WM_DROPFILES
• Add some defines and structures for handling clipboard files
• Add Open and Save dialogs