#422 use foreignObject/div to place actor label in sequence diagram

[whyzdev]

re #422, the change to foreignObject/div is enabled by config.textPlacement: fo. Otherwise, use svg text as before without foreignObject.

_drawTextCandidateFunc may be generalized and used elsewhere in sequence diagram and beyond. there is opportunity to consolidate toward to some common code for text placement.

pased: npm run tape && npm run karma && npm run dist
npm run jasmine was failing unrelated to this change.
manually tested:

   sequenceDiagram
    Alice->>John: Hello John, how are you?
    John-->>Alice: Great!
    very very very long long very long ->> John: ok?

the change may go further to consolidate
\n support.
please let me know if it's better keep going with in this PR, or new PR after the current changeset is satisfied and merged.

[whyzdev]

Please review, but don't merge yet. When config (sequenceDiagram not sequenceConfig) textPlacement is not 'fo', it's not rendering as before. Will fix and check both firefox and chrome some version.

Also saw some other html label config but not used in sequence diagram. will see if/how can consolidate. And some doc out of sync...

Let me know anything else. Thanks,

[knsv]

Much appreciated. Will merge when the build is completed. Seems to take a lot of time, travis might need some configuration. Will try to make a release in dec with the latest changes.

[whyzdev]

Thanks. np, love doing it. Let's see impact to the users.
I am going to continue looking into refactor/consolidate text placement code in sequence diagram and others. Try textwrap attribute as in the existing drawText method used by note etc. Let's keep #422 open.

btw, what do we say about deleting commented and unused code? will go along and see in upcoming PR. Thanks