Improvement/add-methods-consuming-collection

[MicWalter]

Motivation
It should be easy to add a dynamic amount of topics to a Subscribe/Unsubscribe packet or User Properties to any packet.

Resolves #170

Changes
Added methods that consume collection for:

• Mqtt3/Mqtt5 Subscribe Builder
• Mqtt3/Mqtt5 Unsubscribe Builder
• UserProperties Builder

[MicWalter]

Related to #170

[SgtSilvio]

Nice PR 👍
Some general feedback:

• We should take Collection as argument instead of List so passing a Set is also possible
• We should additionally provide methods with an array (varargs) as an argument
• We should additionally provide methods with a Stream as an argument. This allows the user to e.g. specify a list of topic filters with the same QoS:

List<String> topicFilters = Arrays.asList("test", "hello", "world");
MqttQos qos = MqttQos.EXACTLY_ONCE;
Mqtt5Subscribe.builder()
        .addSubscriptions(topicFilters.stream().map(topicFilter -> 
                Mqtt5Subscription.builder().topicFilter(topicFilter).qos(qos).build()))
        .build();

This would also allow us to only take Collection<MqttTopicFilter> and not Collection<String> as argument to addTopicFilters:

List<String> topicFilters = Arrays.asList("test", "hello", "world");
Mqtt5Unsubscribe.builder().addTopicFilters(topicFilters.stream().map(MqttTopicFilter::of)).build();

[SgtSilvio]

See my comment above

[SgtSilvio]

I removed the label and milestone as we have a ticket for tracking this data: #170
PRs are only labelled and included in projects and milestones if no corresponding issue exists, so the PR acts as both ticket and PR.