test-in-docker: quickly test frameworks in docker

This adds `./test-in-docker` for quickly playing with various frameworks.

All the containers are based off Ubuntu 14.04 which has ZSH 5.0.2.

Thanks to @dritter for figuring out all the framework installation
methods.

docker/zplugin/zshrc.plugins

@@ -0,0 +1,5 @@
+#!zsh
+
+zplugin load psprint zsh-navigation-tools
+zplugin load psprint---zprompts
+zplugin snippet ~/p9k/powerlevel9k.zsh-theme