QueryOnClick - keep previous query features

[adube]

Need

We need to have a way to concatenate query results to existing results when using the QueryOnClick widget. For example, the user click somewhere, 10 features are returned. Now, we want to query somewhere else but keep these features.

Solution

• have a special keyboard key triggering the "concatenate" mode while pressed, SHIFT by default
• keep the previous features in the QueryOnClick when in "concatenate" mode
• do not change anything in the result widgets. They will receive the newly concatenated feature list and only show it.
• if using icons, keep them as well

[adube]

Commited in : r1015.