sdss/marvin: Marvin Beta 2.4.0

This release is primarily for DR16+. It adds support for the Visual Morphology VAC. It also adds caching for queries and tools and for various web routes. It contains the following changes

• Adds - caching web routes on Plate, Galaxy pages
• Adds - new use_cache option to Cachable Query class. Implemented in most marvin database calls.
• Adds - most Marvin Tools now use query caching for database calls
• Adds - a new CacheMixIn that adds optional caching to classes utilizing db calls
• Adds - a new Redis dogpile.cache backend; with new regions for Maps and Modelcubes
• Adds - new utility functions for DRPall, and DAPall files, get_xxx_path, get_xxx_file, get_xxx_table
• Adds - adds visual morphology VAC for DR16+
• Fixes - Issue :issue:695 - better web spectra/map error messages;
• Changes - tree and sdss_access submodules to latest 3.0+ and 1.0+ versions
• Changes - path changes to accommodate new tree and sdss_access