Fix coverity hits in Classifier, Decision Forest and GBT

[Vika-F]

Rule of three violations were fixed mostly by adding default implementations or deleting copy constructors and assignment operators.

The default implementations were added into Parameter, Input, InputIface, Model, ModelImpl classes as they are meant to be copy-assignable and copy-constructible.

Non-default implementations of copy constructor and assignment operator were added in GBT ModelImpl and multiclass classifier Model classes because they contain non-POD members.

In the internal classes that do not need to be copyable the copy constructors and assignment operators were deleted.

PR completeness and readability

• I have reviewed my changes thoroughly before submitting this pull request.
• Git commit message contains an appropriate signed-off-by string (see CONTRIBUTING.md for details).
• I have added a respective label(s) to PR if I have a permission for that.
• I have resolved any merge conflicts that might occur with the base branch.

Testing

• I have run it locally and tested the changes extensively.
• All CI jobs are green or I have provided justification why they aren't.

[Vika-F]

/intelci: run