Various changes to modernize the user interface of the Find, Replace, and Find in Files dialogs:

- Got rid of the "close" button, since it is redundant.
- Moved the buttons below the text fields, to make better use of screen real estate.
- Shorten the titles by getting rid of the "Dialog" part.
- Renamed "Search" title to "Find" to match the menu item.
- Renamed "Regular expression" label to the shorter "Regex"
- Added slightly more padding.
- Removed the "Replace+Find" and made "Replace" have this functionality. (all modern editors use Replace to mean "Replace and Find")

The attached png shows the before/after differences in the design of these dialogs.