Update HOXT API to use the builder pattern

[Tibo-lg]

I tried to implement the builder pattern for the HOXT API:

• The AbstractHttpOverXmpp, HttpOverXmppReq and HttpOverXmppResp implement the builder pattern in the same style as ConnectionConfiguration and XMPPTCPConnectionConfiguration.
• The providers had to be refactored to make use of the builders; I had to separate the parsing of headers and data.
• I realized my previous patch did not solve the NullPointerException issue. I updated so that headers is given directly to optAppend but data does not extend Element so it needs an extra if.

[Flowdalic]

Thanks for your contribution. I really appreciate your work and effort towards working together on a HOXT API. +1

I hadn't had a close look at the changes, But could you please

• remove the merge commit (i.e. your work should be (usually) a single commit)
• fix the build errors on java 8 (see travis)

[Flowdalic]

That's an ideal use case for a string switch-case. See (most) other providers for examples.

[Tibo-lg]

remove the merge commit (i.e. your work should be (usually) a single commit)

I fixed that!

fix the build errors on java 8 (see travis)

Should also be fixed.

That's an ideal use case for a string switch-case. See (most) other providers for examples.

Agreed, I had lazily reused the existing code. It is updated now.

[Flowdalic]

Cherry picked as 4d57848

I'd did some further cleaning of the HOXT code based on your commit.

Thank you !