Lots of tidying

- Removed generic `avr8` target
- Simplified AVR8 target construction
- Introduced register descriptor IDs
- Simplified GDB register mappings
- Simplified target interface contract
- Other bits of tidying

src/Insight/InsightWorker/Tasks/ReadTargetRegisters.cpp

@@ -5,6 +5,6 @@ namespace Bloom
     using Services::TargetControllerService;
 
     void ReadTargetRegisters::run(TargetControllerService& targetControllerService) {
-        emit this->targetRegistersRead(targetControllerService.readRegisters(this->descriptors));
+        emit this->targetRegistersRead(targetControllerService.readRegisters(this->descriptorIds));
     }
 }

src/Insight/InsightWorker/Tasks/ReadTargetRegisters.hpp

@@ -10,12 +10,12 @@ namespace Bloom
         Q_OBJECT
 
     public:
-        explicit ReadTargetRegisters(const Targets::TargetRegisterDescriptors& descriptors)
-            : descriptors(descriptors)
+        explicit ReadTargetRegisters(const Targets::TargetRegisterDescriptorIds& descriptorIds)
+            : descriptorIds(descriptorIds)
         {}
 
         QString brief() const override {
-            return "Reading target registers";
+            return "Reading " + QString::number(this->descriptorIds.size()) + " target register(s)";
         }
 
         TaskGroups taskGroups() const override {
@@ -31,6 +31,6 @@ namespace Bloom
         void run(Services::TargetControllerService& targetControllerService) override;
 
     private:
-        Targets::TargetRegisterDescriptors descriptors;
+        Targets::TargetRegisterDescriptorIds descriptorIds;
     };
 }