major LDAviz UI topic index bug (e.g. term, topic, etc.)

[ed9w2in6]

I believe this is a high impact bug as it is not easy to notice, and can lead to incorrect interpretation, especially item 5.

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Steps to reproduce

As of pyldavis==3.4.1, the bug should manifest itself as a minor UI bug (item 2,3), and data inconsistency (item 5).
It can be reproduced as follow:

1. prepare a visualisation with start_index=0
2. click topic 0
3. hover other topic and observe that topic will never be set to color1 (~blue) again, stuck at color2 (~red)
4. clicking other topic and observe same behaviour
5. hover a term and observer radius of topic does not agree with data, in fact, they are off by 1.

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Blame

This commit: 010cde0#diff-12750ebcae02c096cb6939beb54d0ab2353800555b8c01b00fae4fe93f376cfd

reverted some changes that are necessary for non-zero indexing to be functional:
f1cdb65#diff-ce28a7d983569ace041957292840319d65e2c6352989ae5f5556ae555e89404d

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Solutions

The quickest and simplest fix is by reverting changes to all start_index related logic.

However, in the long run, we should probably decouple indexing logic with Topic labels, which will then allow renaming topics, which is sometimes requested by users.

[ed9w2in6]

To mitigate the issue, set start_index=1.