Add commands for managing users to the users app
Import the blobstore file driver by default

It has no external deps and the code is so small that there's no
reason to make the user explicitely import it.
Move gnd.la/bootstrap to gnd.la/frontend bootstrap

This will given us a top level gnd.la package to group all
frontend related stuff.
Move fontawesome assets and functions to its own package
Refactor gnd.la/frontend/bootstrap/form into gnd.la/frontend/bootstrap

The general idea is to end with with frotend packages which encapsulate
all functionality related to that frontend.
Reorder imports
Add html.Attrs.Equal()
Rename constants TYPE_TEXT and TYPE_TAG to TypeText and TypeTag

Introduce also TypeAny, which will be used for upcoming search
support.
Add html.Node.Copy and html.Node.Find
Note that gnd.la/frontend/bootstrap will set the default gnd.la/form renderer
Refactor gnd.la/html/paginator

Simplify the API
Use a pluggable renderer approach, like gnd.la/form. This way
packages can register their own renderers and reusable applications
can just use gnd.la/html/paginator directly and let the final app
decide which frontend framework to use.
Format imports
Format imports
Fix typo in comment
Add support for the email input type in forms

Enabled from the email form tag. Validated by default unless the
novalidate tag is provided.
Update messages.pot file for the form package
Change the CSRF error message to use the "form" context
Update messages.pot file for package form
Load messages from the _messages directory rather than .

This fixes the problem where compiling messages for a package would
recurse into its subpackages. Also, make the directory name configurable
using a command option.
Add a debug message for each .po file compiled into messages