Add an option to Conflicter to copy changes/content back to the template

[mshima]

Overview of the feature request

Changes to JHipster templates usually are implemented in the resulting application and then ported to the template.
We can improve templates development by adding an option to copy the content back to template.

• try to apply the diff changes.
• if diff doesn't apply copy the full content.

Motivation for or Use Case

Make easier to develop templates.

Related issues or PR

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