Merge pull request #3738 from dimagi/fix-fixture-api

catch error during fixture api call
unused import
basic end to end support of making fixture upload asynchronous

is heavily modeled off other bulk upload code/uis
move additional error handling and feedback to the asynchronous ui
wording change
remove unused code
do initial validation of file format in the synchronous UI, cleanup
add more up front validation and cleanup
add progress bar support
add staging.yaml to the repo
add async fixtures to staging yaml
use file in the repository

simplify
remove stale branch
remove missing branch
show echange tab only for users that can edit apps or commcare users
Applications / Survey tab should have the same viewing permissions as Exchange tab
fix security holes in app manager. read only / reporting users should not be allowed to view the applications tab or access its contents
remove login_and_domain_required if require_can_edit_apps is used
restore functionality to disable upload button until a file is selected
fix empty DELETE_HEADER bug