[MWAR-445] Create war archive without creating exploded war

**[wei cai](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=wecai)** opened **[MWAR-445](https://issues.apache.org/jira/browse/MWAR-445?redirect=false)** and commented

Currently to build a war archive, maven-war-plugin need:
* source paths (libraries, src/main/webapp...) -> exploded war -> build archive

Many files need to be copied to exploded war directory before creating war archive.

To speed up the maven-war-plugin, I would like to propose below solution:
* source paths (libraries, src/main/webapp...) -> build archive

Here when "-Dmaven.war.exploded.skip=true" is passed, the maven-war-plugin then build the archive directly based on all source paths, in this way, massive file copying can be avoided.

maven.war.exploded.skip is by default set as false as there might be a few cases user want an exploded war, for example:
* Using tomcat7-maven-plugin to start exploded webapp

I created the PR: https://github.com/apache/maven-war-plugin/pull/21 for initial discussion.

Please help review and advise:
* Does it make sense to skip the creation of exploded war? Any features will break because of this?
* Regarding the ITs, shall I separate the tests into 2 scenarios?
* ITs for original behavior.
* ITs for building war archive without creating exploded war.

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**Affects:** 3.3.2