Decode special characters when copying grid cells

[insmac]

Currently, if the value of a given cell contains special characters (i.e. <, > or &), they will be copied in their HTML-encoded form, thus preventing using the value for things like SQL filters.

The cell value should be decoded upon writing its contents to the clipboard.

Steps to replicate:

CREATE TABLE chars (char string);
INSERT INTO chars (char) VALUES ('&');
INSERT INTO chars (char) VALUES ('<');
INSERT INTO chars (char) VALUES ('>');
SELECT * FROM chars;

Then, copy any cell to clipboard and paste elsewhere.