Update LCAOTDDFT documentation

Update LCAOTDDFT documentation:

• describe up-to-date (easier, more efficient) parallelization settings
• improve Ag55 tutorial
  • split the workflow (ground-state, time-propagation, spectrum)
  • use realistic parameters
  • use p-valence basis sets by default
  • add comparison between different basis sets
  • make basis-set-generation example less prone to errors
• remove out-dated, unused scripts
• use stricter ground-state convergence in all the scripts