logic: Added update checker connecting to online API

* connects to https://www.sourcetrail.com/api/v1/versions/latest
* sends information about OS, platform, license type, current version and a unique user token
* Automatic update check is enabled via Startscreen and performed once every 24 hours on window focus
* Update check can be forced by clicking on "check for new version" on start screen
* renamed TimePoint to TimeStamp

fortune cookie message = In Träumen und im Leben ist nichts unmöglich.

src/lib/settings/ApplicationSettings.h

@@ -5,6 +5,8 @@
 
 #include "settings/Settings.h"
 
+class TimeStamp;
+
 class ApplicationSettings
 	: public Settings
 {
@@ -117,6 +119,15 @@ public:
 	int getAcceptedEulaVersion() const;
 	void setAcceptedEulaVersion(int version);
 
+	std::string getUserToken() const;
+	void setUserToken(std::string token);
+
+	bool getAutomaticUpdateCheck() const;
+	void setAutomaticUpdateCheck(bool automaticUpdates);
+
+	TimeStamp getLastUpdateCheck() const;
+	void setLastUpdateCheck(const TimeStamp& time);
+
 	// network
 	int getPluginPort() const;
 	void setPluginPort(const int pluginPort);