[#745] Add exclude keyword option to Akvo Pages

On Akvo Pages, a boolean field 'exclude_keywords' has been added. When set to False (default), the keywords act as usual. However, when set to True, projects with the indicated keywords will be excluded from the project list on the Akvo Page.

E.g. For the YEP Water page, we want to exclude the internal Akvo projects. By setting this option to True and indicating a new keyword ('akvo internal') on both the Akvo Page and the internal Akvo project(s), the project will not be shown on YEP's page.
[#745] Added migration for partnersite.exclude_keywords
[#745] Update help texts about project selection for Sites
[#748] Continent code for 'BQ' added
[#710] Fix ProjectResource.get_object_list()

ProjectResource.get_object_list() does not return unpublished projects
when the API is queried by an authenticated user.

Fix by calling ApiKeyAuthentication.is_authenticated() to check if the
user is authorized to view unpublished projects.
[#710] Fix RainActivity.rsr_id() and RainActivity.internal_id()

The xpath for those two methods is searching from the root (xpath search
string starts with "//") in the belief that the tree only encompassed
one activity. But this seems not to be the case resulting in _all_
activities being searched.

Fix by removing the "//".
[#710] Add more settings

Add settings for the URLs to use when fetching the RAIN organisations
and activities XML.

Add settings for a pair of log labels.
[#710] Add functions for importing XML from file system or internet.

Add load_xml(). This function is moved from rain_project_upload.py

Also add save_xml() to allow saving of the fetched XML for logging
purposes.
[#710] Better logging for organisation_upload.py
[#710] Import organisation XML from URL

Fetch organisation XML from the RAIN website.

The XML fetched is saved for logging/debugging in the same folder as the
import logfiles.
[#710] Import activities XML from URL

Fetch activities XML from the RAIN website.

The XML fetched is saved for logging/debugging in the same folder as the
import logfiles.
[#710] Better logging for post_import.py
[#710] Add category, sync_owner and publishing

Add methods for setting the category, sync_owner and publishing status
of all imported RAIN projects.
[#710] Import activities XML from URL

Fetch activities XML from the RAIN website.
Merge pull request #750 from akvo/feature/748_country_admin

[#748] Continent code for 'BQ' added
Merge pull request #746 from akvo/feature/745_exclude_keywords

[#745] Add exclude keyword option to Akvo Pages
Merge pull request #755 from akvo/hotfix/710_rain_iati_import

[#710] rain iati import
[#756] Release notes for hotfix 2.4.2
[#756] Release notes for hotfix 2.4.2 - update
Merge pull request #757 from akvo/develop

[#756] Astana hotfix 2.4.2