implement text highlighting

[Iyusuf40]

• now we can use ctrl-A to highlight all text
• batch edit highlighted text
• use ctrl-C and ctrl-V to copy to and from textShape

[gniziemazity]

Didn't quite get why a separate undo / redo system is needed for text. I assume it is so the text element stays selected and editing happens more smoothly. But it was not clear in your description, so I ask.

[Iyusuf40]

Yes, I should have mentioned.

• The text shape is having the undo and redo methods because the HistoryTool's undo and redo unselects the text, going out of the current edit mode.
• I tried to modify it to use the HistoryTool's methods but it was difficult to get right, then I tried implementing it using the Cursor class, but then the histories are lost after a new text is selected.
• This was a simple albeit not so clean way to handle each text's histories even after editing other texts.
• In addition, I also changed the hittest drawing for texts to use a rectangle, because the fillText method of ctx do leave out spaces undrawn, causing missed text selection.
• In general, I think much of the code could be structured better.