Help menu

Created a [help manual](https://github.com/CherimaeNemeta/PlasmaGraph/blob/help_menu/plasmagraph/src/HelpManual/HelpManual.java) and implemented it as a [help menu](https://github.com/CherimaeNemeta/PlasmaGraph/blob/help_menu/plasmagraph/src/org/pvg/plasmagraph/views/MainView.java)