Added in-function documentation and arguments for apply_length_resolved.m

The documentation for apply_length_resolved was extended to contain all
input and output arguments, and nboot (number of bootstrap samples for
bootstrapping procedure) was added as an optional input argument.
Error message in central video evaluation function has been removed.

Inside a parfor loop, a value (this_target_folder) was assigned inside
of a try statement. This lead to a warning that the variable might not
be assigned in every parfor loop iteration, potentially leading to a
run-time error when value would not be assigned but requested.

Fixed by moving outside of the try statement. Any requests of values
from this_target_folder are still contained within the try statement,
still preventing errors for one video to disrupt the entire analysis of
a batch.