New features:
- the plot.dpi configuration option sets the dpi of produced rasterized
  figures
- the --fraction option of the time command specifies what fraction at
  the end of the temporal series should be represented
- StepsView have a meaningful repr

Dependencies:
- loam minimum version bumped to 0.3.0

Bug fixes:
- reading of fields spread across nodes on more than one direction was
  failing in HDF5 format, this is now fixed
- time series and profiles extra names deduced from HDF5 files were
  binary string, they are now decoded to UTF8 format
- field plots in cartesian geometry have now a tighter layout
- the label on colorbars is now horizontal
- the plot.style option now works as intended