Linux packaging

Fixes linux packaging and adds a new "linux_standalone" target.
> so probably adding the include $(ROOT_DIR)/make/tools.mk after that line would work and be cleaner


```
diff --git a/Makefile b/Makefile
index c8e3ba7..22bf3d6 100644
--- a/Makefile
+++ b/Makefile
@@ -990,10 +990,10 @@ endif
 
 .PHONY: package
 package:
-       $(V1) cd $@ && $(MAKE) --no-print-directory $@ QT_PLUGINS_DIR="$(QT_PLUGINS_DIR)"
+       $(V1) cd $@ && $(MAKE) --no-print-directory $@
        
 linux_standalone:
-       $(V1) cd package && $(MAKE) --no-print-directory $@ QT_PLUGINS_DIR="$(QT_PLUGINS_DIR)"
+       $(V1) cd package && $(MAKE) --no-print-directory $@
 
 .PHONY: package_resources
 package_resources:
diff --git a/package/Makefile b/package/Makefile
index bbdc086..c7b097d 100644
--- a/package/Makefile
+++ b/package/Makefile
@@ -10,6 +10,7 @@
 # Locate the root of the tree
 WHEREAMI := $(dir $(lastword $(MAKEFILE_LIST)))
 ROOT_DIR := $(realpath $(WHEREAMI)/../)
+include $(ROOT_DIR)/make/tools.mk
 
 # Set up some macros
 BUILD_DIR    := $(ROOT_DIR)/build
```
ends with
```
linux_standalone starting
Copying Qt5 plugins libraries
cp: cannot stat ‘/imageformats’: No such file or directory
make[1]: *** [linux_standalone] Error 1
make: *** [linux_standalone] Error 2
```