Small IDE improvements

[kallisto56]

Hi there,

This pull-request contains next set of improvements:

• Line numbers in error messages copied from ErrorsPanel were starting from zero. It's fixed now.

• ErrorsPanel now has an identical to CallStackPanel feature, allowing copying errors into clipboard using Ctrl+C hotkey.

• Instead of removing intersecting cursors, they are now merged on a condition that at least one of them has a selection. Cursors without selection will not be merged even if they sit on the same position, because there is rare case, when this is useful, here is an example:

no-selection--no-merge.mp4

• AutoComplete had an issue when typing full name of the member and then selecting suggestion. For example: typing Swap! and then hitting Enter, will insert suggestion which would result in Swap!Swap!;
• AutoComplete now moves cursors at the end of the inserted string, if cursor was at the start of the suggestion, example:

AutoComplete-from-front.mp4

Last commit is me forgeting to check if insertStr is null or not.

[kallisto56]

Something is not quite right, I'll close this pull-request in order to figure out what is wrong and make a new one.