review: refactor Environment to add encoding

[surli]

Add encoding in Environment and use it in CompilationUnit#getOriginalSourceCode()
Fix #1497

[msteinbeck]

How about using Charset instead of a String?

[surli]

How about using Charset instead of a String?

Done.

[spoon-bot]

Revapi Analysis results

Old API: fr.inria.gforge.spoon:spoon-core:jar:5.9.0-20170807.224502-32

New API: fr.inria.gforge.spoon:spoon-core:jar:5.9.0-SNAPSHOT

Detected changes: 2.

Change 1

Name	Element
Old	none
New	method java.nio.charset.Charset spoon.compiler.Environment::getEncoding()
Code	java.method.addedToInterface
Description	Method was added to an interface.
Breaking	binary: non_breaking,

Change 2

Name	Element
Old	none
New	method void spoon.compiler.Environment::setEncoding(java.nio.charset.Charset)
Code	java.method.addedToInterface
Description	Method was added to an interface.
Breaking	binary: non_breaking,

[monperrus]

add test?

[spoon-bot]

Revapi Analysis results

Old API: fr.inria.gforge.spoon:spoon-core:jar:5.9.0-20170817.224439-43

New API: fr.inria.gforge.spoon:spoon-core:jar:5.9.0-SNAPSHOT

Detected changes: 2.

Change 1

Name	Element
Old	none
New	method java.nio.charset.Charset spoon.compiler.Environment::getEncoding()
Code	java.method.addedToInterface
Description	Method was added to an interface.
Breaking	binary: non_breaking

Change 2

Name	Element
Old	none
New	method void spoon.compiler.Environment::setEncoding(java.nio.charset.Charset)
Code	java.method.addedToInterface
Description	Method was added to an interface.
Breaking	binary: non_breaking