Collective.documentgenerator

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- Clean notes when creating/editing a `PODTemplate` this way the `search&replace`
functionnality works as expected:

- Added `utils.clean_notes`;
- Clean notes is only done if `odt_file` changed and file is updated only if
something was cleaned;
- Moved function `create_temporary_file` from `events.styles_events` to `utils`.

[gbastien]

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- Use wrapped context of ProxyObject for __unicode__ method.
Revert __repr__ to default implementation.
[sdelcourt]

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- Require `beautifulsoup4<4.10` in `setup.py` as starting from 4.10.0,
`beautifulsoup4` is no more compatible with `Python2`.
[gbastien]
- Pass parameter `html=True` when calling `Renderer` so content is considered
as html when using `xhtml` function in POD template, some pre-processing is
applied to ensure that given content is valid xhtml.
[gbastien]
- Use wrapped context of ProxyObject for __repr__ and __str__ methods.
[sdelcourt]

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- Allow templates selection on the search result before applying the replace.
[sdelcourt]

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- Added a view to search and replace in POD templates pod expressions `collective.documentgenerator-controlpanel`.
[aduchene]
- Added an helper class `SearchAndReplacePODTemplates` that can search and replace in POD templates pod expressions.
[aduchene]
- Added tests on search and replace feature.
[aduchene]
- Added utility classes to search and replace pod expressions in ODT files.
[sdelcourt]
- Added a script `bin/search_replace` to search and replace in ODT files via CLI.
[sdelcourt]
- Added some documentation about search and replace feature.
[aduchene]
- Added `portal` to the default generation context.
[gbastien]
- Fix style update temporary file directory didn't use CUSTOM_TMP.
[odelaere]
- Ensure CUSTOM_TMP directory exists before rendering a document.
[odelaere]

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- Added a view to check up every POD templates `check-pod-templates`.
[odelaere]
- Adapted the `check-pod-templates` way to `find_pod_templates` to take into
account current context. This way, we may check pod templates on a
particular folder.
[gbastien]
- Corrected domain
[sgeulette]
- Don't check by default selection column in dg-templates-listing to avoid
user error with batch buttons
[sgeulette]