MRG: Replace tempita with Jinja2

[hoechenberger]

Fixes #10204

WIP:

• Render tutorial
• Remove tempita from HTML templates for Jupyter
• Changelog entry

Nice: VS Code has debugging support for Jinja templates:

[hoechenberger]

One circle job failed because MNE-BIDS depends on our vendored Tempita. This will require an update of MNE-BIDS and can be ignored here for now.

All other checks passed.

I will update the changelog ASAP; in any case, this PR is ready for review.

• Removed Tempita in favor of Jinja2
• HTML repr of Info is more robust
• I could remove some manual string escaping from the Python code, as Jinja2 will do that work for us now
• All HTML templates are now located under mne/html_templates

Built doc artifact: https://40576-1301584-gh.circle-artifacts.com/0/dev/index.html

[larsoner]

I think the only thing missing is we need to add jinja2 to README.rst and setup.py, but I've added them to my TODO list for #10199 since I need to update them there anyway. Otherwise this LGTM, so +1 for merge from my end.

[jasmainak]

This broke mne-bids :)

In [1]: import mne_bids
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-1-b553cc368f26> in <module>
----> 1 import mne_bids

~/Documents/github_repos/mne-bids/mne_bids/__init__.py in <module>
      3 __version__ = '0.10.dev0'
      4 from mne_bids import commands
----> 5 from mne_bids.report import make_report
      6 from mne_bids.path import (BIDSPath, get_datatypes, get_entity_vals,
      7                            print_dir_tree, get_entities_from_fname,

~/Documents/github_repos/mne-bids/mne_bids/report.py in <module>
      9 
     10 import numpy as np
---> 11 from mne.externals.tempita import Template
     12 from mne.utils import warn, logger, verbose
     13 

ImportError: cannot import name 'Template' from 'mne.externals.tempita' (unknown location)

[hoechenberger]

This broke mne-bids :)

Already fixed: mne-tools/mne-bids#944