* [Companion] On first use of Companion show preferences dialog and new welcome message (closes#4731); Improve detection of new version upgrade & reformat message; Add download link URL to Linux update notice (closes#4774); Fix issue with leftover top-level settings categories when checking for older versions which don't exist; Introduce basic structure for warnings/messages to be suppressed by user preferences (eg. "don't show this message again" option).
* Welcome msg typo fix.
