Fix MR Selection, Go Code Refactor (#358)

refactor: Refactors the Go codebase into a more modular and idiomatic approach
fix: require selection of specific MR when there are multiple targets for a given source branch
feat: Allows for the passing of Gitlab's filter options when choosing an MR, improves MR selection
feat: API to choose an MR from a list based on the provided username's involvement as an assignee/reviewer/author

This is a #MINOR release

cmd/app/members.go

@@ -0,0 +1,65 @@
+package app
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"github.com/xanzy/go-gitlab"
+)
+
+type ProjectMembersResponse struct {
+	SuccessResponse
+	ProjectMembers []*gitlab.ProjectMember
+}
+
+type ProjectMemberLister interface {
+	ListAllProjectMembers(pid interface{}, opt *gitlab.ListProjectMembersOptions, options ...gitlab.RequestOptionFunc) ([]*gitlab.ProjectMember, *gitlab.Response, error)
+}
+
+type projectMemberService struct {
+	data
+	client ProjectMemberLister
+}
+
+/* projectMembersHandler returns all members of the current Gitlab project */
+func (a projectMemberService) handler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	if r.Method != http.MethodGet {
+		w.Header().Set("Access-Control-Allow-Methods", http.MethodGet)
+		handleError(w, InvalidRequestError{}, "Expected GET", http.StatusMethodNotAllowed)
+		return
+	}
+
+	projectMemberOptions := gitlab.ListProjectMembersOptions{
+		ListOptions: gitlab.ListOptions{
+			PerPage: 100,
+		},
+	}
+
+	projectMembers, res, err := a.client.ListAllProjectMembers(a.projectInfo.ProjectId, &projectMemberOptions)
+
+	if err != nil {
+		handleError(w, err, "Could not retrieve project members", http.StatusInternalServerError)
+		return
+	}
+
+	if res.StatusCode >= 300 {
+		handleError(w, GenericError{endpoint: "/project/members"}, "Could not retrieve project members", res.StatusCode)
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
+
+	response := ProjectMembersResponse{
+		SuccessResponse: SuccessResponse{
+			Status:  http.StatusOK,
+			Message: "Project members retrieved",
+		},
+		ProjectMembers: projectMembers,
+	}
+
+	err = json.NewEncoder(w).Encode(response)
+	if err != nil {
+		handleError(w, err, "Could not encode response", http.StatusInternalServerError)
+	}
+}