Issue #39 - new UI for search, confirm and progress bar for the merging process

Thanks to @jhoopes and @ndunand, I have revisited the code and place it here for your revision.

This is related to issue #39.

New UI to include: 

* Search for users to merge.
* Confirmation step, with a latter popup, to actually proceed with the merging.
* Progress bar added.
* Javascript to control the radiobuttons when selecting users to merge.

The progress bar includes 3 steps:

1. To search for users to merge, or to update the current selection, even if both users are selected.
1. To visualize the two users to merge as confirmation step. This also includes a popup to really confirm that action. From here, we can remove the current selected users and come back to step 1. We also allow to go back to step 1 to update any of them without removing selected users (button cancel).
1. To show merging log. When pressing button, this brings the user to the step 1. This may also solves issue #43.