Created a generic array class.

src/Array.cpp
  - Created generic Array class
  - Declaration and definition in same file due to template
Changed m_basic to use Array<BasicEntity> instead of BasicEntity**

include/App.h
  - Changed m_basic from BasicEntity** to Array<BasicEntity>*
  - Removed m_num_entities, m_capacity for m_basic

src/App.cpp
  - Changed m_basic to use pointer notation and Array<BasicEntity> functions
  - App now allows for many more circles to be placed instead of 10