DownloadFileTask: Support redirection across schemes (e.g. HTTPS to HTTP)

Android's HttpURLConnection does not redirect across schemes even if
set(Instance)FollowRedirects() is set to true, so add a manual fallback.
Merge pull request #32 from sschuberth/develop

DownloadFileTask: Support redirection across schemes (e.g. HTTPS to HTTP)
Update README.md
DownloadFileTask: Recursive resolving of redirects across schemes
AsyncTaskUtils for switching between execute and executeOnExecutor
Merge pull request #34 from bitstadium/feature/recursiveredirect

DownloadFileTask: Recursive resolving of redirects across schemes
Merge branch 'feature/taskexecute' into develop

Conflicts:
	src/main/java/net/hockeyapp/android/tasks/DownloadFileTask.java
Also support "long" app sizes when parsing JSON

The DownloadFileTask already supports "long" for the total file size, so
we should do so here, too.
Fix the timestamp to be parsed as "long" instead of "int"
Initially show the size as unknown for external builds of size 0
Remove a redundant variable initialization in DownloadFileTask
Generalize DownloadFileTask a bit so it can be more easily extended
Add a GetFileSizeTask to determine the file size of externally hosted APKs
Merge pull request #37 from sschuberth/develop

Support determining the APK file size for external builds via the HTTP header
Update version of annotations dependency.
Bump version number.
Update copyright.
Fixes for Android L.

Map L to version 5.0.
Fix for unknown sources detection.
Update docs.
Update LICENSE