Feature/ineqs

[FBumann]

New class Inequation

Split up the classs Equation in 3 Classes:

• Abstract class _Constraint
• class Equation(_Constraint)
• class Inequation(_Constraint)

Benefits

• Identification of Constraint kind simpler and without string comparison (.eq_type=='eq').

• Trailing Changes

• attribute .eqs or .equations is renamed to .constraints
• properties for Equations and Inequations rely on constraints with instance checks. This leads to more, but simpler and more concise properties
• This might induce performance issues (they should be negligible)

  Other Changes

• Bugfix of not showing No. of Inequations
• No of Equations does not longer contain No of Inequations --> Benefit
• Changed some more information strings and code to create them