Rename ContentTypes to CONTENT_TYPES (+7 squashed commits)
Squashed commits:
[442c2a2] Fix style errors
[655267b] Fix typo related to old naming
[7e09ff3] Now using a private static final InmutableMap

Also fixed class origin typo.
[c517aa5] Add import for com.google.common.io.Files
[e85f6de] Fix class typo
[d082b91] Update AbstractUpload.java

Now using String.getFileExtension
[7602a33] Fix style errors

/scratch/jenkins/workspace/plugins/google-storage-plugin/src/main/java/com/google/jenkins/plugins/storage/AbstractUpload.java:30: Wrong order for 'java.util.Hashtable' import.
/scratch/jenkins/workspace/plugins/google-storage-plugin/src/main/java/com/google/jenkins/plugins/storage/AbstractUpload.java:413:22: ',' is not followed by whitespace.
/scratch/jenkins/workspace/plugins/google-storage-plugin/src/main/java/com/google/jenkins/plugins/storage/AbstractUpload.java:413:66: ',' is not followed by whitespace. (+1 squashed commit)
Squashed commits:
[09a989b] Add support for Content-Type web-related detection.