templater: rename "right" argument of pad() function Before, right=True meant right justify, which I think is left padding.

templater: make pad() evaluate boolean argument (BC) Otherwise it would crash if template expression was passed. This patch unifies the way how boolean expression is evaluated, which involves BC. Before "if(true)" and "pad(..., 'false')" were False, which are now True since they are boolean literal and non-empty string respectively. "func is runsymbol" is the same hack as evalstringliteral(), which is needed for label() to take color literals.

templater: fix if() to not evaluate False as bool('False') Before, False was True. This patch fixes the issue by processing True/False transparently. The other values (including integer 0) are tested as strings for backward compatibility, which means "if(latesttagdistance)" never be False. Should we change the behavior of "if(0)" as well?