Add the possibility to create terminal tabs with different terminal content

[pommepommee]

• added JavaScript script to change terminal tab

• when changing tab, it changes the active tab, the command written in the terminal (in the example cat tab1.txt) but also the terminal content

• changed some size values

• added margin:0 ;padding:0; to body because #container{ height: 100vh; } creates an extra scrollbar.

[fobabs]

@pommepommee @thomasgigout The idea of the project is to use just HTML and CSS. We could add a JS functionality later in the future.