Remove fixsystem from the build system

New feature / build system update:

• Removes fixystem script from the build system #870
  • This removes all compiler dependencies in the code; DART code no longer needs to be changed with fixsystem (by commenting in/out blocks of code for NAG, gfortran)
  • mkmf + fixsystem are also no longer reliant on the FC variable in the makefile being the name of the compiler
  • The mpi utilities mods are no longer automatically edited upon running quickbuild with certain compilers, therefore messing up your git working tree.
  • NOTE this does NOT change the way in which the user builds DART or interacts with DART

Bug-fixes:

• Read state before broadcasting single value state space inflation #1130
  • Fixes logic in which files to read for prior and posterior inflation
• Removes "ifort" from build_everything as it is no longer supported on Derecho

Documentation update:

• Updates the custom.css to use Poppins font #1135

What's Changed

• Fixsystem removal by @mjs2369 in #1121
• Read state before broadcasting single value state space inflation, correct logic for which files to read by @hkershaw-brown in #1133
• doc: custom.css to use Poppins font by @hkershaw-brown in #1136

Full Changelog: v11.24.1...v11.25.0