Version bump: v2.0.8

Click handlers and backend processing for assessment mode

README sections about localization

[SOL-1944] Submit Answer UI

[#SOL-1944] Review notes: responsiveness, ARIA attributes, focus after reset

Revert "Add some documentation of assessment mode to README.md."

Add some documentation of assessment mode to README.md.

Move items between zones in assessment mode

Child elements of items can get removed/reordered, so we have to mark
each of them children with a unique key for virtual dom to be able to
reorder them correctly.

The absence of keys was causing some weird glitches where the content
would disappear while the item spinner was visible.

In standard mode, once you drop an item into the correct zone, you can
no longer move it until you reset the exercise.

In assessment mode, we want users to be able to freely move items
between zones until they explicitly submit their solution.

This commit implements the ability to move dropped items between zones
in assessment mode. It does not make any changes to standard mode.

Keep items in dropped position in assessment mode.

Items dropped onto wrong zones in standard mode are immediately removed
from the board and sent back to the bank.

In assessment mode, items should stick in the dropped position until the
entire problem is explicitly submitted by clicking a button.

This commit only implements the "stick" part, but does not implement the
submit button and associated handler.

This commit also fixes an existing bug where the template function
would gett reused between blocks.

The template function (which is slightly different for each block,
depending on block's configuration) was getting assigned to the global
DragAndDropBlock function. Each block would overwrite the previous
value, which caused bugs.

Add option for limiting number of attempts in assessment mode to Studio editor

Allowing items to have more than one permitted target zone

- Wrapp input field for max_attempts in label to be able to use classes instead of ids.

Remove support for numerical input

Nobody is using it anymore and it adds a lot of complexity to the
codebase.

Mode field: Help string improvement

Problem mode field and edit capabilities

Revert "Mode field"

Mode field

Nobody is using it anymore and it adds a lot of complexity to the
codebase.

update the version in setup.py