Add "Iterate" flow/connector support in Component Framework

According to https://help.talend.com/display/TalendOpenStudioforDataIntegrationUserGuide62EN/4.4.1+Connection+types

there are following connection types in Talend Studio:
1. Row connection
2. Iterate connection
3. Trigger connection
4. Link connection

Row connections are:
1.1 Main
1.2 Lookup
1.3 Filter
1.4 Reject
1.5 ErrorReject
1.6 Output
1.7 Uniques/Duplicates
1.8 Multiple Input/Output
1.9 Combine

Trigger connections are:
3.1.1 On Subjob Ok
3.1.2 On Subjob Error
3.1.3 Run if
3.2.1 On Component Ok
3.2.1 On Component Error
3.2.2 Run if
where 3.1 - subjob triggers, 3.2 - component triggers

I'm not sure whether all of them are often used, but I know that "Iterate" flow is often used.
For example, it is used in tDropboxList, tFlowToIterate, tS3List, tGoogleDriveList components.
Above *List components have no Main flow and schema. They have only Iterate flow. They provide data throw so-called Flow variables.
Following is job example, where Iterate flow is used:
tDropboxList ->(Iterate) tFixedFlowInput -> tLogRow
For each retrieved record tDropboxList emits a set of flow variables, which can be used in subsequent components.
They can be used as column values. For example, ((String)globalMap.get("tDropboxList_1_PATH"))