editor: added button for block removal
editor: added popup support, added new tab support, redesigned some visual elements a bit
editor: removed initial mockup content, added init() and hooked to onload
editor: renamed all the create_*_tab() to tab_create_*()
editor: added handling of the case with no tabs
editor: rearranged tab_create_*() functions
editor: the newly created tab is now selected by default
PackedEditor, editor: added PakcedEditor.removeBlock(), created block_remove(), moved away block_add() to a separate function
editor: renamed parameters when calling a PackedEditor method "i", "order" to "position"