Timeline tool should work with SVs containing `__`

For example, SDG stat-var `sdg/SE_ADT_ACTS.AGE--Y_GE75__SEX--F__TYPE_OF_SKILL--SKILL_ICTTRFF` has `__` which is the stat-var delimiter on timeline tool.

We should change that so this link will work: https://dev.datacommons.org/tools/timeline#statsVar=sdg/SE_ADT_ACTS.AGE--Y_GE75__SEX--F__TYPE_OF_SKILL--SKILL_ICTTRFF&place=country/BRA