Feature: Reachable states

[frippe75]

Might be a duplicate of #61

It would be nice to be able to reach different progress states using a new method "moveTowards()".
moveTowards() would provide a way to animate the progressbar towards percentages but not overrunning them to better model what is going on if the progressbar is modelling a few states.

I'm using it for a firmware update process:

• STATE_FIRMWARE_DOWNLOAD = moveTowards(10%)
• STATE_FIRMWARE_INSTALLING = moveTowards(30%)
• STATE_FIRMWARE_REBOOTING = moveTowards(50%)
• STATE_FIRMWARE_DONE = moveTowards(100%)

This would make the progressbar better aligned with what is actually happning. Given that the process is somewhat deterministic.

moveTowards() should start out being 100% to keep current feel of ngProcess.

In my case the download phase is quick and the reboot slow. Makes in more linear so that the user can estimate the time to completion.

Also... My AngularJS skills is not a stage where I'm able to do a PR for you ... sorry.

[frippe75]

Made a small change adding a setter function. If you want me to do a PR please let me know a suiteable name of the function ..

This is what it looks like in my example have four fixed states to process. I think I will look into adding the css part to make some markers where the "towards"/states are on the progressbar.

Did not play too much with my different states-procentages but it's a pretty linear feel to the process
youtube example of a firmware upgrade