Theme system

Solves #1

Can choose between QtCreator's themes and base Vivy theme, or system's theme.

Depends on !21 (merged)

src/Lib/Log.cc

@@ -3,7 +3,6 @@
 using namespace Vivy;
 
 LogSink::~LogSink() noexcept {}
-
 LogMessage::~LogMessage() noexcept { parentLogger->sendLogMessage(*this); }
 
 std::shared_ptr<LogSink>
@@ -15,6 +14,12 @@ LogSink::newSink() noexcept
     return std::make_shared<makeSharedEnabler>();
 }
 
+void
+LogSink::registerLoggerClient(std::shared_ptr<Logger> logger) noexcept
+{
+    clientLoggers.push_back(logger);
+}
+
 void
 LogSink::closeLoggerClient(Logger *const logger) noexcept
 {
@@ -41,8 +46,8 @@ Logger::logEvent(const char *fileName, const char *functionName, const int lineN
 }
 
 void
-Logger::sendLogMessage(const LogMessage &msg) const noexcept
-{
+Logger::sendLogMessage(const LogMessage &msg) const noexcept {
+    TODO(Write the code to send the event...)
 }
 
 LogMessage::LogMessage(Logger *const logger, const LogMessage::Header hdr) noexcept