Rephrase the tooltip of Reload Cache to avoid confusion
Summary: The action is Reload Cache, but the tooltip used to say Rebuild instead of Reload, which caused some confusion among translators (https://www.transifex.com/wildfire-games/0ad/translate/#sv/$/113848525), and hence could have the same effect among users.
Test Plan: No tests, only user-visible strings are affected.
Reviewed By: Imarok
Differential Revision: https://code.wildfiregames.com/D2294