add charset support to thymeleaf template, change default charset from system default charset to utf-8

[gitSquirel]

add charset support to thymeleaf template, change default charset from system default charset to utf-8

Motivation:

Thymeleaf template use system default charset to read template file, so it behave differently on different OS, since utf-8 is commonly used for source file, so I change the default charset to utf-8, and add a ThymeleafTemplateEngine.create method with Charset parameter to meet who don't use utf-8.

Conformance:

Your commits should be signed and you should have signed the Eclipse Contributor Agreement as explained in https://github.com/eclipse/vert.x/blob/master/CONTRIBUTING.md Please also make sure you adhere to the code style guidelines: https://github.com/vert-x3/wiki/wiki/Vert.x-code-style-guidelines

[pmlopes]

Hi @gitSquirel can you please sign the Eclipse ECA. When you do, please do a rebase and push and we can merge your enhancement!

[vietj]

@gitSquirel please sign the ECA agreement and reopen a new PR