Update on help management

src/main/java/ui/tree/HelpTree.java

src/main/java/ui/tree/JDiagramTree.java

src/main/java/ui/window/JFrameHelp.java

src/main/resources/help/diplodocus.html

src/main/resources/help/diplodocus.md

src/main/resources/help/general.html

src/main/resources/help/general.md

src/main/resources/help/none.html

src/main/resources/help/none.md