user-accounts: Remove unused MAXNAMELEN definition

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Make UmAccountDialog a GtkDialog

The dialog will get much more complex due to 'enterprise login'
work and we want a proper object here.

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Don't refer to UmAccountDialog as um

It's confusing to read; it reads as 'user manager'. Since this
is a GObject, just use self as customary.

Most of these lines change in later commits anyway, so this won't
really polute the 'git blame'

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Cleaner interaction with UmAccountDialog actions

More clear scoping and interaction with running actions in
UmAccountDialog. In later 'enterprise login' patches we have long
running actions that's why this needs cleaning up.

In particular:

 * Show errors as children of the dialog.
 * Errors don't make the account dialog go away, user can correct
   problems.
 * Use more standard GAsyncResult style callbacks:
   um_account_dialog_perform() um_account_dialog_finish()
 * Disable controls while the operation is happening.

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: User to cancel long actions in UmAccountDialog

Allow the user to cancel long actions in UmAccountDialog by
pressing the cancel button.

This is relevant in later commits when we merge 'enterprise login'
support.

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Show a spinner during account dialog actions

During actions which can run a long time show a spinner
indicating that something is going on.

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Add test tool frob-account-dialog

A simple tool to show the add account dialog for quick
iterations testing of the 'enterprise login' functionality.

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Title of accounts dialog becomes "Add Account"

This title makes sense for both remote and local users. In the
case of remote users we're not creating accounts, we're just
adding them to the system.

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Port account dialog to GtkGrid

Some spacing issues will be sorted in a later commit.

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Fix memory leak of GtkBuilder in accounts dialog

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Separate local account stuff in accounts dialog

Separate the local account stuff a bit so when the enterprise
stuff comes in it's still readable.

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Cleaner validation and validate on open

Clean up the validation so we can plug in the enterprise
login stuff. Also fix a bug where the dialog was not
validated when it was initially opened.

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Add switcher between modes

Add the switcher between the local account and enterprise
modes.

The enterprise area just has a place holder widget for now.

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Add um_user_manager_cache_user()

This calls the AccountsService.CacheUser() method to register
a user that's not in /etc/passwd

Depends on:

https://bugs.freedesktop.org/show_bug.cgi?id=50770

https://bugzilla.gnome.org/show_bug.cgi?id=677548
user-accounts: Implement enterprise logins in add dialog

 * Use realmd for domain joining and lookup, runtime dependency
 * Validate join domain correctly
 * Add UmRealmManager for handling some stuff above the autogenerated
   realmd dbus code
 * Show a dialog if the user's credentials cannot be used to join
   the domain. Prompt for admin creds.
 * Register the user's login with the AccountsService
 * This depends on the CacheUser() method of AccountsService

https://bugzilla.gnome.org/show_bug.cgi?id=677548