[#27] Auto refresh folder view

[urfdvw]

issue: https://github.com/urfdvw/CircuitPython-online-IDE2/issues/27

This is achieved by checking if the folder tree is changed. The tree is constructed from the root.

MISC

• also check if the current folder is still there, if not, back to root.
• changed some defaults,
  • especially not hiding the 'x' when file changed. That will cause trouble if that is a deleted file.

[urfdvw]

Wil not merge now, this is costing too much CPU on low spec machines. To be specific: On N5000 laptop with fan cooling, cost about a constant 20% cpu power.

[urfdvw]

Found out it is OK to not check before each periodic update. Checking itself is costing lot of resource.