Make thumbnails generation of RAW images 2 times faster

When a RAW file is detected, sets the plugin quality for speed. Some example of speed improvements (time in ms) below.

Default quality:

• 3173 "RAW_APTUS_75.MOS"
• 2162 "RAW_CANON_EOS_5DMARK3.CR2"
• 4929 "RAW_CANON_EOS_5DS.CR2"
• 11434 "RAW_FUIJI_X-E2.RAF"
• 1500 "RAW_SONY_A900.ARW"

Quality 1 (this patch):

• 1640 "RAW_APTUS_75.MOS"
• 1397 "RAW_CANON_EOS_5DMARK3.CR2"
• 2775 "RAW_CANON_EOS_5DS.CR2"
• 273 "RAW_FUIJI_X-E2.RAF"
• 769 "RAW_SONY_A900.ARW"