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Added notes about the default technology stack.
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Added MySQL to the default technology stack list.
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Cleaned up default technology stack requirements.
Removed an unused dependency and added an index.

An unused dependency, Guava, has been removed.

An index has been added to increase the speed of mobility/dates/read.
Merge branch 'ohmage-2.16' of github.com:ohmage/server
Optimized mobility/dates/read.

Added an optimization to mobility/dates/read to vastly improve read times in most cases.

Closes #622
Merge branch 'ohmage-2.16' of github.com:ohmage/server
Fixed a bug with writing images.

When transforming the images, the type was always being set to JPEG. If an image was not a JPEG and could not be transformed into a JPEG (e.g. because it had a transparent element), this wou
ld cause an exception to be thrown. Now, it will write the transformed images in the same format as the original.

Closes #625
Merge branch 'ohmage-2.16' of github.com:ohmage/server
Merge branch 'master' of github.com:ohmage/server into ohmage-2.16-user_setup_password