ref(Dockerfiles): base Dockerfiles on ubuntu:14.04

To avoid current and future versioning headaches with **deis/base** and proposed alternatives, this changes Deis' docker components to use **ubuntu:14.04** directly. `docker pull|push` of our images will still benefit from cached layers, but the burden is on us now to keep their initial stanzas consistent with each other.

Also:
- updated the component README.md files, no more trumpeting of "Trusted Builds"
- standardized on `curl` instead of `wget`
- updated our `pip` installs to 1.5.6.

**NOTE:** updating deis/database from precise to trusty changed the uid/gid of the postgres user--will this cause problems for existing deis-database-data containers?

Closes deis/base#7, deis/base#13, deis/base#14, refs #1861.

@aledbf we have to add the Docker repository before we do the apt-get update, to pull in its packages, if that's what you were asking. I was hoping to merge this in time for 0.12.0 since there's already so much change happening, but I still need to fix something, and others may not want to merge it yet.