review: refactor MethodTypingContext#isOverriding moved to ClassTypingContext

[pvojtechovsky]

Possible solution of #1292

[spoon-bot]

Revapi Analysis results

Old API: fr.inria.gforge.spoon:spoon-core:jar:5.7.0-20170514.224530-96

New API: fr.inria.gforge.spoon:spoon-core:jar:5.7.0-SNAPSHOT

Detected changes: 3.

Change 1

Name	Element
Old	method boolean spoon.support.visitor.MethodTypingContext::isOverriding(spoon.reflect.declaration.CtMethod<?>)
New	none
Code	java.method.removed
Description	Method was removed.
Breaking	source: breaking,

Change 2

Name	Element
Old	method boolean spoon.support.visitor.MethodTypingContext::isSameSignature(spoon.reflect.declaration.CtMethod<?>)
New	none
Code	java.method.removed
Description	Method was removed.
Breaking	source: breaking,

Change 3

Name	Element
Old	method boolean spoon.support.visitor.MethodTypingContext::isSubSignature(spoon.reflect.declaration.CtMethod<?>)
New	none
Code	java.method.removed
Description	Method was removed.
Breaking	source: breaking,