Added makefile target for installing project in editable mode.

Without this it is not possible to use command line interface on our automated build system. (Redmine issue: #3387)

Makefile

@@ -99,6 +99,7 @@ help:
 	@echo "  * $(GREEN)deps-lwchroot$(NC): creating local lightweight chroot subdirectory structure"
 	@echo "  * $(GREEN)deps-python$(NC): install Python dependencies"
 	@echo "  * $(GREEN)deps-python-dev$(NC): install Python development dependencies"
+	@echo "  * $(GREEN)deps-editable$(NC): installing project in editable mode"
 	@echo "  * $(GREEN)deps-python-upgrade$(NC): upgrade Python dependencies to latest versions"
 	@echo "  * $(GREEN)deps-python-upgrade-dev$(NC): upgrade Python development dependencies to latest versions"
 	@echo "  * $(GREEN)deps-webui$(NC): install web interface dependencies"
@@ -201,7 +202,7 @@ develop: FORCE
 #
 # Install and configure project dependencies.
 #
-deps: deps-prerequisites deps-lwchroot deps-python deps-python-dev deps-webui deps-geoip deps-negistry deps-postgresql translations-compile
+deps: deps-prerequisites deps-lwchroot deps-python deps-python-dev deps-editable deps-webui deps-geoip deps-negistry deps-postgresql translations-compile
 
 #
 # Cleanup development and build environment.
@@ -287,6 +288,13 @@ deps-python-dev: FORCE
 	@$(PIP) install -r conf/requirements-dev.pip
 	@echo ""
 
+#
+# Install project in editable mode.
+#
+deps-editable: FORCE
+	@echo "\n$(GREEN)*** Installing project in editable mode ***$(NC)\n"
+	@$(PIP) install -e ".[dev]"
+
 #
 # Upgrade project`s Python dependencies using pip requirements file to latest
 # versions.
@@ -559,7 +567,6 @@ build-package-deb: FORCE
 	@grunt deb-build
 	@echo ""
 
-
 # Empty rule as dependency will force make to always perform target
 # Source: https://www.gnu.org/software/make/manual/html_node/Force-Targets.html
 FORCE: