Revert "Merge pull request #148 from Logan676/camera"

This reverts commit 6e3fb44e56d331ba3aca0166afbaa598e5d585d5, reversing
changes made to 43535712ba5c47649a0a14ac8cb49d2ff8e38f95.
apply Guava's static collections utilities
Merge pull request #160 from Logan676/guava

apply Guava's static collections utilities
mark code that need improvement with "XXX"
fix camera photo upload cancell all error

only cancel camera upload tasks exclude other file upload tasks  when user stops camera upload service
code cleanup
code refactor