Implement receiver HID++ connect/disconnect events

Many changes were made here but that was the biggest one.

There's currently a bug where std::system_error: Broken pipe is thrown
after launching the daemon with a receiver connector.

A workaround for this bug is to simply shake the mouse while starting
the daemon. I will investigate this soon.

src/logid/backend/hidpp20/EssentialFeature.cpp

@@ -0,0 +1,44 @@
+#include <cassert>
+#include "EssentialFeature.h"
+#include "feature_defs.h"
+#include "features/Root.h"
+
+using namespace logid::backend::hidpp20;
+
+std::vector<uint8_t> EssentialFeature::callFunction(uint8_t function_id,
+        std::vector<uint8_t>& params)
+{
+    hidpp::Report::Type type;
+
+    assert(params.size() <= hidpp::LongParamLength);
+    if(params.size() <= hidpp::ShortParamLength)
+        type = hidpp::Report::Type::Short;
+    else if(params.size() <= hidpp::LongParamLength)
+        type = hidpp::Report::Type::Long;
+
+    hidpp::Report request(type, _device->deviceIndex(), _index, function_id,
+                          LOGID_HIDPP_SOFTWARE_ID);
+    std::copy(params.begin(), params.end(), request.paramBegin());
+
+    auto response = _device->sendReport(request);
+    return std::vector<uint8_t>(response.paramBegin(), response.paramEnd());
+}
+
+EssentialFeature::EssentialFeature(hidpp::Device* dev, uint16_t _id) :
+    _device (dev)
+{
+    _index = hidpp20::FeatureID::ROOT;
+
+    if(_id)
+    {
+        std::vector<uint8_t> getFunc_req(2);
+        getFunc_req[0] = (_id >> 8) & 0xff;
+        getFunc_req[1] = _id & 0xff;
+        auto getFunc_resp = this->callFunction(Root::GetFeature, getFunc_req);
+        _index = getFunc_resp[0];
+
+        // 0 if not found
+        if(!_index)
+            throw UnsupportedFeature(_id);
+    }
+}