Changed MainView structure to resemble RequirementsManager

Made the structure more simlar to RequirementsManager's MainView class (used tabAdd method to add tab). The structure is also more like RequirementsManager's in the fact that the main panel extends JTabbedPane rather than the previous JPanel, then the content is contained in separate classes.
Merge branch 'sbl-dev' of git://github.com/struct-by-lightning/wpi-suite into sbl-dev
Fixed imports in MainView.java
Merge pull request #52 from ZPak/sbl-dev

Changed MainView structure to resemble RequirementsManager