Editing text clipboard field

[mlewand]

It should be possible to edit textual clipboard entries.

I think that it's viewer that should provide a binding to a proper editor.

There could be an "edit" button. After clicking it the viewer text would be transformed into a textarea with current value preset.

Here is the list that could be added at the beginning:

• Text (plain text area)
• Hex
• HTML (e.g. using Monaco)

[mlewand]

Note that if #45 lands before this issue, any editing should invalidate hashes for a given snapshot object.