Workspace management

[craxal]

This issue tracks all items related to managing a user's "workspace" in Storage Explorer, including:

• The set of Quick Access items
• The set of attachments
• User settings
• Open tabs and selections (colors)
• Other preferences and session data
• Syncing workspace data across devices

Managing workspaces is such that designing and implementing an unified underlying architecture would greatly ease the development of individual features involving the above areas.