There is no doubt the Las Vegas Raiders have improved their roster over the last four days. General manager John Spytek and his staff made 10 selections during the NFL draft and have been adding to their rookie class with a slew of undrafted free agents since the event concluded on Saturday. While it’s probably not a championship-caliber roster yet, the Raiders are moving in the right direction. Here are five things that were learned about the organization over the past few days: 1. There’s a new face of the franchise Fans have been operating under the assumption Fernando Mendoza would be the quarterback of the future since watching him win the national championship in Miami back in January. The fact that it’s now official hasn’t seemed to dampen the enthusiasm. There was an electric atmosphere around the team facility when he was introduced Friday, starting with a pep rally-like entrance for him and his family as they pulled up and walked through the front door.…