fix(manager): add stub for context with Manager

This adds testing fixtures for the manager. It includes a stub context
that has either default or stub implementations for each object.

WIP: Frame out repo package and modify charts package to support chart download

fix(Makefile): Install Glide with go get -u

Add vim scratch files to gitignore

go get -u is used to install and handle the other dependencies,
such as gox, golint, and vet. Use the same method for Glide.

add repo cmds to helm client

* use pkg/httputil instead of func in helm client

fix(Makefile): add flake8 to bootstrap

flake8 support was recently added, but the bootstrap didn't check or
install it.

fix(manager): use decoder

ref(*): remove punctuation at end of error

ref(*): remove reference to latest

This is because the marshals traverse structs in field order, and
it makes more sense for the fields to have status first and details
second.

Instead of repeating io.Read/Unmarshal pattern, use the Decoder,
which also gets us content-type negotiation.

This adds a Content-Type-sensitive decoder for HTTP requests.

fix(manager): remove backend variable

This replaces the backend global variable with the Context.Manager
variable.

Add chart representation to types.go

docs(README): update README in light of merger

fix(Makefile): print error if pip is missing

Also add an example.

This strips the README back to an accurate representation of the current
state of the project. We can begin adding to it again as it
re-stabilizes.

fix(devtools): prevent start-local.sh from killing process

Also, prompt the user to run pip install during bootstrap.

Closes #362.

fix(manager): update routes and error handling