ui: Show news sent with update check on start screen

* News are passed as JSON string, containing an array of news items.
* Each news item has version and content (html).
* Items can be filtered by min/max version, OS and license. The first item that fits is used.
* Items can be important, which highlights the news box.
* News are not shown if older than 5 days.

fortune cookie message = You will be financially successful in case your actions are well planned.

src/lib/settings/ApplicationSettings.cpp

@@ -597,6 +597,16 @@ Version ApplicationSettings::getUpdateVersion() const
 	return Version::fromString(getValue<std::string>("user/update_check/update_version", "2017.1.0"));
 }
 
+std::string ApplicationSettings::getUpdateNews() const
+{
+	return getValue<std::string>("user/update_check/news", "");
+}
+
+void ApplicationSettings::setUpdateNews(const std::string& news)
+{
+	setValue<std::string>("user/update_check/news", news);
+}
+
 void ApplicationSettings::setUpdateVersion(const Version& version)
 {
 	if (version.isValid())

src/lib/settings/ApplicationSettings.h

@@ -167,6 +167,9 @@ public:
 	Version getUpdateVersion() const;
 	void setUpdateVersion(const Version& version);
 
+	std::string getUpdateNews() const;
+	void setUpdateNews(const std::string& news);
+
 	bool getSeenErrorHelpMessage() const;
 	void setSeenErrorHelpMessage(bool seen);