Filter dialog improvements

Improvements to filter dialog inspired by ux#166 (closed)

Addresses ux#178

• Filter selection moved to a popover
• Effects are listed in a popup menu and can be selected by searching (by name)
• Adjusted connector sizes to make them more compact
• Fixed an issue where all parameters would initially be visible in a docked filter dialog
• Dialog definition moved (partially) to Glade file
• Fixed min size of parameters panel to make it fit in a narrow docked dialog
• Reactive layout to accommodate wide dialog
• Added primitive filter attributes to fe-image and fe-tile (#1417)
• Replaced GTK color picker with Inkscape color picker
• Sources can now be hidden (for most use cases only the source graphics is useful; other inputs are broken or need ux work)