Make inputs more flexible

[hanslovsky]

#41 introduced the option to use /paintera-raw-dataset/data/s0 as input for conversion to a Paintera raw data set located at /paintera-raw-dataset and re-use s0. This should be extended to label data as well, and could also be used to "repair" existing datasets, e.g. when label data becomes inconsistent during a failed canvas commit. To make this happen, the following changes need to be implemented:

1. Allow input to be any of (auto-detect the correct input from this)
   • /paintera-raw-dataset/data/s0
   • /paintera-raw-dataset/data
   • /paintera-raw-dataset
2. Add fully-functional overwrite option (requires Support removing blocks n5#55, Add N5Writer.deleteBlock n5#58)