branches: reduce nesting in for loop

i18n: use datapath for i18n like for templates and help To avoid circular module dependencies we initialize i18n from util when datapath is found.

help: don't search randomly for help data - trust util.datapath The search was introduced in c904e76e3834 without a convincing explanation why it should be necessary ... except for consistency with templater handling. Now, just keep it simple.

templater: don't search randomly for templates - trust util.datapath The search was introduced in 2653740d8118. It might have been necessary back then when using __file__ directly and frozen-ness wasn't considered. Now we should know exactly where the templates can be found.

templater: inline global 'path' list in templatepaths

templater: introduce templatepaths for getting paths searched for templates Avoid function with different return types depending on parameters.

util: introduce datapath for getting the location of supporting data files templates, help and locale data is normally stored as sub folders in the directory containing the source of the mercurial module. In a frozen build they live as sub folders next to 'hg.exe' and 'library.zip'. These different kind of data were handled in different ways. Unify that by introducing util.datapath. The value is computed from the environment and is always used, so we just calculate the value on module load.

util: move _hgexecutable a few lines, closer to where it is used

hgk: define bookmark colour explicitly, as Tk 8.6 has changed their meaning

largefiles: remove 'forget' list that's always empty