refactor: add explicit this-> where possible

I have knowingly skipped some files/portions of files where this would
create merge conflicts for other open PRs.

src/common/Channel.cpp

@@ -451,7 +451,7 @@ IndirectChannel::IndirectChannel(ChannelPtr channel, Channel::Type type)
 
 ChannelPtr IndirectChannel::get() const
 {
-    return data_->channel;
+    return this->data_->channel;
 }
 
 void IndirectChannel::reset(ChannelPtr channel)

src/common/SignalVectorModel.hpp

@@ -138,7 +138,7 @@ public:
             return QVariant();
         }
 
-        return rows_[row].items[column]->data(role);
+        return this->rows_[row].items[column]->data(role);
     }
 
     bool setData(const QModelIndex &index, const QVariant &value,

src/common/WindowDescriptors.cpp

@@ -300,7 +300,7 @@ void WindowLayout::activateOrAddChannel(ProviderId provider,
                 this->score += 2;
                 if (split.channelName_ == this->spec)
                 {
-                    hasChannel = true;
+                    this->hasChannel = true;
                     if (!split.filters_.empty())
                     {
                         this->score += 1;