Clone block variables

[JPBetley]

Uses the same functionality from cloneRow to index variables inside blocks when using the cloneBlock function.

Before, variables inside cloned blocks would result in the same variable name used multiple times:

Template: cloneBlock('CLONE', 3)
${CLONE}
${variable}
${/CLONE}

Result:
${variable}
${variable}
${variable}

Now, in the same style of cloneRow, the variables are indexed:

Template: cloneBlock('CLONE', 3)
${CLONE}
${variable}
${/CLONE}

Result:
${variable#1}
${variable#2}
${variable#3}

[troosan]

duplicate of #459, but I'll merge this one as #459 is too old to merge