M2002-2010: Add models from book ‘L. Edelstein-Keshet: Mathematical Models in Cell Biology’ (Contributed/CPM/... Contributed/ODE/..., Contributed/PDE/...)

Multiple models from Leah's book.

• Corresponding issue: #20

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• M2002 (CPM/One CPM Cell)
• M2003 (CPM/One Random Walker)
• M2004 (ODE/Integrate and Fire)
• M2005 (ODE/Fitzhugh–Nagumo ODEs)
• M2006 (CPM/Two CPM Cells Adhesion)
• M2007 (CPM/Cell Sorting (LEK))
• M2009 (PDE/Schnakenberg System)
• M2010 (CPM/Chemotaxis)