0.4.0

Markers section, saved filter management, more scene editing

• Add a Markers browse section and a Markers tab on tag pages
• Create, update, rename and delete saved filters from the browse menu
• Edit a scene's studio, galleries and groups (with scene number)
• Keep animated tag images (GIF/WebP/APNG) animated in the image cache;
  clear the old cache once on upgrade
• Use the Stash logo in the sidebar and setup screen
• Keep focus on toolbar buttons when the grid reloads
• Update README; bump version to 0.4.0