Spurious deprecated to string call (issue #212)

[HenkPoley]

Adds a test for the erroneous 'Deprecated __toString call' warning for code like (string)$another->returnsBlaFoo(); I src/test/kotlin/com/funivan/idea/phpClean/inspections/toStringCall/ToStringCallIssue212Test.kt

Attempts to fix the issue inside buildVisitor() and visitPhpMethodReference() overrides in src/main/kotlin/com/funivan/idea/phpClean/inspections/toStringCall/ToStringCallInspection.kt

Should fix Issue #212. But I'm not too familiar with this codebase.