Update all usage of "server" lp to "nw-lp"

This change is made for consistency across all configuration files
and workload generators in core CODES. Where older models and versions
of CODES utilized the "server" identifier to specify the number of
server LPs per modelnet group repetition, newer models and
configurations utilized the less paradigm specific "nw-lp" identifier.

This shift slightly fractured the codebase and led to confusion when
running similar/same configurations across different network models.

Specifically, this change converts all usage of the "server" identifier
to the "nw-lp" identifier. All tests, existing default configuration
files, and models have been updated to use the "nw-lp" identifier for
the workload server LPs. Some docs and readmes have been updated as well
to no longer instruct new users to use the "server" identifier.

Updated congestion control in dragonfly: now messages are saved in a waiting list at the routers in case of buffer overflows

Tired of explaining that it's not a good representation of a WAN. Instead, it's
now a simple point-to-point latency/bandwidth model.

All configuration now proceeds on a per-LP level, and requires separate
registration and configuration calls, as seen in the test programs.
model_net_set_params is no longer used, and is replaced by model_net_register
and model_net_configure. The dragonfly network, having two LP types bundled in
the same code-path, is special-cased in the registration code.

LP-mapping in model-net now has the following defaults:
- counts via codes_mapping_get_lp_count are now with respect to the calling
  network LP's annotation.
- when looking up network LPs via
  codes_mapping_get_lp_info/codes_mapping_get_lp_id, the annotation of the
  calling network LP is used. Hence, routing now occurs only between LPs of the
  same annotation. If the destination LP's group specified by model_net_*event
  does not contain a modelnet LP with the same annotation as the modelnet LP in
  the sender's group, then an error will occur (in codes_mapping).

Known Issues:
- modelnet users currently cannot specify which modelnet LP to use in the case
  of multiple modelnet LPs in the sender's group. This will be fixed in future
  commits after a consensus is reached on the best way to expose this
  information.