Upgrade to Scala 2.13

[GreyCat]

• Bump Scala version to 2.13 (as 2.12 has been deprecated and is no longer supported — https://www.scala-lang.org/download/all.html
• Fix incompatibilities and deprecations which prevented project from compiling

[GreyCat]

Previous master build results:

[info] Total number of tests run: 1261
[info] Suites: completed 14, aborted 0
[info] Tests: succeeded 1200, failed 61, canceled 0, ignored 0, pending 0
[info] *** 61 TESTS FAILED ***
[error] Failed tests:
[error] 	io.kaitai.struct.translators.TranslatorSpec
[error] 	io.kaitai.struct.translators.TypeDetector$Test
[error] 	io.kaitai.struct.ErrorMessagesSpec

This build after Scala 2.13 upgrade and some extra fixes:

[info] Total number of tests run: 1261
[info] Suites: completed 14, aborted 0
[info] Tests: succeeded 1200, failed 61, canceled 0, ignored 0, pending 0
[info] *** 61 TESTS FAILED ***
[error] Failed tests:
[error] 	io.kaitai.struct.translators.TranslatorSpec
[error] 	io.kaitai.struct.translators.TypeDetector$Test
[error] 	io.kaitai.struct.ErrorMessagesSpec

Looks like we're maintaining status quo and should not make situation worse.