various: encapsulate all code in the olive namespace to avoid name collisions

Large-scale code cleanup. Also adds a license to the top of all files that were
missing it.

app/common/timecodefunctions.cpp

@@ -24,6 +24,8 @@
 
 #include "config/config.h"
 
+OLIVE_NAMESPACE_ENTER
+
 QString padded(int64_t arg, int padding) {
   return QStringLiteral("%1").arg(arg, padding, 10, QChar('0'));
 }
@@ -273,3 +275,5 @@ int64_t Timecode::rescale_timestamp_ceil(const int64_t &ts, const rational &sour
 {
   return qCeil(static_cast<double>(ts) * source.toDouble() / dest.toDouble());
 }
+
+OLIVE_NAMESPACE_EXIT