1345: Alert styles and wrapper

There is currently variation in how alerts are displayed across the UI. Most of the technical work in this ticket is creating a wrapper around bootbox.alert

The major change is in where alerts are used in OpenLMIS — they should only be used when a user is forced to acknowledge an action — such as a page the user is forbidden from seeing or a response from a service that is a non-trivial error (500 errors)

Note that a success alert has not been added — there should be no reason to create this style of alert

This ticket has three main components:

1. Create an AlertFactory, that documents when and how to use alerts
2. Create a styleguide page that shows stylistic variations of alerts (info and error)
3. Update the use of alerts in the OpenLMIS-UI codebase

Each method of the Alert factory should return a promise which is resolved when the alert is closed by the user. When used in a controller the Alert factory should work like:

// Normal alert
var promise = Alert('message.language.key', 'Additional information can be entered as an optional second argument');

// Error alert (with callback)
Alert.error('message.language.key').then(function(){
    // do something else
});