Move to new Package for Maven Central Prep

This pull request includes a bunch of changes that move the package from com.slidingmenu.* to com.jeremyfeinstein.slidingmenu.* 

Changes Include: 

- Package Rename
- Import renames
- Folder Structure now matches new package name com/jeremyfeinstein/slidingmenu/
- Migration to src/main/java folder structure for Maven Standard Directory Layout
- Updates to gitignore to ignore DS_Store and target/ directory

While I know this change is a breaking change to the library, it is a change that needs to be done eventually as the package name is currently com.slidingmenu which is parked at a domain warehouse which I've contacted already and have not heard back from yet (minimum bid at the time of writing this was 1K for the domain - which is a bit absurd to spend, IMO, for an open source project). 

Once this type of change happens I will help publish it to Maven Central with Jeremy