makefile: remove Ubuntu Yakkety and Zesty docker targets Yakkety (16.10) was supported until 2017-07-20 and Zesty (17.04) was supported until 2018-01-13.

merge: use operation-provided labels (ex: dest/source) in several merge-tools Tools that did not use labels already, used only one, or used some label other than the exact strings of "local" or "other" were unmodified. Cases that used the label "base" were modified as well, if they were otherwise changed in this CL; "merged" was *not* changed. There are other possible changes we might want to make, but I didn't: - bcompare (linux and osx) uses the labels "parent1" and "parent2" instead of "local" and "other", so it was left alone, even though beyondcompare3 (windows) *was* changed. - araxis used the labels "Other", "Base", and "Local :$local", so it was also left alone. - UltraCompare didn't provide a label for 'local', just for 'base' and 'other', so it was left alone. Differential Revision: https://phab.mercurial-scm.org/D2012

filemerge: support passing labels to external merge tools This adds $labellocal, $labelother, and $labelbase to the replacement set for merge-tools.<tool>.args config variables, and to the environment as HG_MY_LABEL, HG_OTHER_LABEL, and HG_BASE_LABEL, respectively. We also add merge-tools.<tool>.mergemarkers and merge-tools.<tool>.mergemarkertemplate config variables as counterparts of the variables available in [ui]. We are intentionally *not* respecting ui.mergemarkers when calling out to external merge programs; too often the default template will be too wide to display comfortably in most GUIs. Differential Revision: https://phab.mercurial-scm.org/D2011