Prepare PTScotch integration

See merge request !202

This is useful to check mesh partition/load balance

- Add simple CMake recipe
- Add PartitionerOptions
- Separate ParMETIS partitioner from Partitioner

Feature/eigen3

See merge request !201

This kind of boundary condition type is useful for PN solvers for instance.

- the environment variable PUGS_INSTALL_DIR is no more used
- also fix HDF5 detection on ubuntu for plugins

Change strategy for modules registration to the ModuleRepository

See merge request !200

Plugins are loaded through environment variables. Two environment
variables are read: PUGS_PLUGIN and PUGS_PLUGIN_DIR

- PUGS_PLUGIN is a string literal that contains the filename of the
dynamic library that contains plugins. One can provide multiple
filename using semicolumn separators.
  ex. PUGS_PLUGIN="/path/to/my/libplugin1.so;/anotherpath/to/another/libplugin2.so"

- PUGS_PLUGIN_DIR is a string literal that contains directory path
where plugins (dynamic libraries) are.  One can provide multiple path
using semicolumn separators. All the dynamic libraries present at the
locations are loaded!
  ex. PUGS_PLUGIN="/path/to/a/plugin/list/;/anotherpath/to/another/plugin/list/"

Now modules register self register: ModuleRepository is unchanged
while adding new modules

Integrate checkpointing

See merge request !199

This is a raw copy from `feature/composite-scheme`

Also plug to checkpointing and add related tests

Add TinyMatrix's double-dot product

See merge request !198