Centralize logic to get current server time

A few different implementations of computing the current time were
spread out through the code base, most of them using gettimeofday().

This centralizes the logic in CUtil::GetTime() for easier maintenance,
and also allows all call sites to get the benefit of the clock_gettime()
code path on systems that support it.

src/Buffer.cpp

@@ -37,12 +37,7 @@ CBufLine::CBufLine(const CString& sFormat, const CString& sText,
 CBufLine::~CBufLine() {}
 
 void CBufLine::UpdateTime() {
-    timeval tv;
-    if (0 != gettimeofday(&tv, nullptr)) {
-        tv.tv_sec = time(nullptr);
-        tv.tv_usec = 0;
-    }
-    m_Message.SetTime(tv);
+    m_Message.SetTime(CUtils::GetTime());
 }
 
 CMessage CBufLine::ToMessage(const CClient& Client,