Consolidate 'search' and 'transfer' into a single Django app

[NickolausDS]

Originally, I conceived the portal to be composed of smaller standalone apps where developers would pick and choose which app best suited their needs. 'search' and 'transfer' would be completely decoupled apps and contain their own views, models, and templates and could be seamlessly combined with Django URLs. The actual framework turned out very different from that idealized conception.

A 'transfer' app with views and urls doesn't currently exist, as there hasn't been a need for a standalone transfer app. The current 'search' app directly integrates transfer functionality for both Globus Transfer and Preview. While the internal search/transfer components are fully decoupled, the out-of-the-box search portal depends heavily on transfer.

I propose getting rid of both globus_portal_framework.search and globus_portal_framework.transfer and combining them. This would cause breaking changes but make several things cleaner:

• It would consolidate separate app 'settings.py' files
• Tests would be simplified due to only referencing a single settings file (e.g. override_settings will work seamlessly again)
• The directory structure would be simplified, removing a depth layer of directories
• The two separate utils.py modules would be renamed to more sensical search.py, transfer.py, preview.py modules

This would cause breaking changes for downstream projects that called into apps for specific functionality instead of using the top level includes. For example, from globus_portal_framework.search.utils.default_search_mapper instead of from globus_portal_framework import default_search_mapper

[NickolausDS]

Done in #38