standardize gather technology tooltips
This patch standardizes the tooltips of gather technologies, per https://trac.wildfiregames.com/wiki/EnglishStyleGuide#Stats
Flavour text strings are moved from the "tooltip" to the "description" entry.
Test Plan: Check for mistakes and omissions.
Reviewed By: Gallaecio
Differential Revision: https://code.wildfiregames.com/D2253