[gui] Log window inconveniences

[CmP-lt]

Using log window becomes inconvenient when it needs to be opened and closed multiple times because:

• each time new log window is created;
• previously opened log windows need to be closed manually to avoid having many log windows that are all brought to foreground when new log window is created;
• log window gets blocked by main window when the former is sent to background, i.e. need to minimize main window or adjust it's size and/or position to be able to access existing log window.

There would be no such inconveniences if only one log window, that would be brought to foreground when called, could be created.

[skylot]

@CmP-lt sure! I agree that it will be nice to:

1. force only one log window at a time
2. bring it to front if it opens from menu/toolbar action
3. convert dialog to window, so it will appear in windows taskbar (like it is done for search dialog)

[skylot]

Fixed in PR #1649 by @jpstotz