add Level Versions

[KeppyMarbles]

Features:

• Implemented "Update level" button on the level page, which brings you to the level upload page.
• Updated the level page to display all previous versions and their changelog.
• Added a modal on the level page for curators to view which accounts voted what.

Internal changes:

• Updated the level upload page to do level updating (write changelog, don't add to pack) if an update id is provided
• Added "pastVersions" property to missions to store info about a previous version
• Added "currentVersion" and "currentVersionChangelog" property to missions
• Updated MissionUpload::submit to accept an existingLevelId. If provided, a previousVersion is created and the updated level is stored in a folder named: {levelId}-v{version} in the same directory.
• Updated deleteSingleLevel to delete all pastVersion mission directories.
• Updated /api/level/:levelId/zip and /api/level/:levelId/mbpak to accept a level version number.
• Updated DownloadButton to use a "version" field
• Added optional "updateId" to MissionUpload constructor to prevent duplicate mis error (in case the user didn't change the .mis when updating)
• Changed ExtendedLevelInfo.curatorVotes to return ProfileInfo instead of user id.