git-gui: Avoid using the term URL when specifying repositories
Instead, 'Location' is used to label such inputs; in the Clone dialog,
'Source' and 'Target' are also introduced to further clarify the situation.
The intent is to increase GUI consistency in the case location templates
(upcoming) are used - then, other locators than URL may be used.
Signed-off-by: Petr Baudis <petr.baudis@novartis.com> Signed-off-by: Shawn O. Pearce <spearce@spearce.org>