Hotfix/bugs on wordnet app

[StephanHasler]

This pull request resolves two bugs in the wordnet_app (#3002 and #3003).

[arademaker]

I am assuming the use of HTML in the code like

nltk/nltk/app/wordnet_app.py

Line 897 in 4616bcd

template = """

is because NLTK is avoiding have to depend on web frameworks like Flask right?

[StephanHasler]

I guess the use of a web framework like Flask could lead to less and simpler code. I would prefer that.
The question is, if it makes sense to port the wordnet_app. It seems no one uses it. The wordnet online search is more informative. I used the wordnet_app only once when the online search was not available.

[arademaker]

Hi @StephanHasler, I am curious, what 'wordnet online search' are you using?

1. The Princeton web interface for PWN 3.1 at https://wordnet.princeton.edu?
2. The http://en-word.net from the Open English WordNet (fork from Princeton WN 3.0/3.1) from @jmccrae ?
3. The multilingual http://compling.hss.ntu.edu.sg/omw/ from @fcbond ?
4. The Polish/English wordnets interface at http://plwordnet.pwr.wroc.pl/wordnet/?

I also have my own web interface for the Portuguese Wordnet and Princeton English Wordnet 3.0 at http://openwordnet-pt.org.

[StephanHasler]

I use the princeton Web interface. I was not aware of the others.
I would not have fixed the wordnet_app, if I knew the alternatives, e.g. Open English Wordnet.
Thanks for telling me!

[purificant]

LGTM

I was able to reproduce both of #3002 and #3003 and the change set in this PR prevents the issues from occurring in my testing.

[tomaarsen]

I trust your judgement on this @purificant. Beyond that, these changes seem sensible when inspected.
I appreciate your work on this @StephanHasler! Especially the latter bug seems nasty to chase down.