Repository: 12rambau/sepal_ui

Issue:
sepal_ui.Btn does't work as expected 
I want to create a simple Icon button, to do so:

```python
sw.Btn(icon=True, gliph ="mdi-plus")
```
Doing this, without "msg" parameter will add the default text to the button which is "click", I think is worthless having that value.

So if I want to remove the default text, I would expect doing this:
```python
sw.Btn(children = [""], icon=True, gliph ="mdi-plus")
# or 
sw.Btn(msg= ""] icon=True, gliph ="mdi-plus")
```

Which leads the icon aligned to the left  and not centered (as it is using a empyt string as message).


Discussion:

Patch:
diff --git a/sepal_ui/sepalwidgets/btn.py b/sepal_ui/sepalwidgets/btn.py
index 137622fa..105f6160 100644
--- a/sepal_ui/sepalwidgets/btn.py
+++ b/sepal_ui/sepalwidgets/btn.py
@@ -25,6 +25,9 @@ class Btn(v.Btn, SepalWidget):
 
     .. deprecated:: 2.13
         ``text`` and ``icon`` will be replaced by ``msg`` and ``gliph`` to avoid duplicating ipyvuetify trait.
+
+    .. deprecated:: 2.14
+        Btn is not using a default ``msg`` anymor`.
     """
 
     v_icon = None
@@ -36,7 +39,7 @@ class Btn(v.Btn, SepalWidget):
     msg = Unicode("").tag(sync=True)
     "traitlet.Unicode: the text of the btn"
 
-    def __init__(self, msg="Click", gliph="", **kwargs):
+    def __init__(self, msg="", gliph="", **kwargs):
 
         # deprecation in 2.13 of text and icon
         # as they already exist in the ipyvuetify Btn traits (as booleans)
@@ -55,7 +58,7 @@ class Btn(v.Btn, SepalWidget):
                 )
 
         # create the default v_icon
-        self.v_icon = v.Icon(left=True, children=[""])
+        self.v_icon = v.Icon(children=[""])
 
         # set the default parameters
         kwargs["color"] = kwargs.pop("color", "primary")
@@ -89,6 +92,7 @@ class Btn(v.Btn, SepalWidget):
         Set the text of the btn
         """
 
+        self.v_icon.left = bool(change["new"])
         self.children = [self.v_icon, change["new"]]
 
         return self


Test patch:
diff --git a/tests/test_Btn.py b/tests/test_Btn.py
index fcaed760..4e3cb9b5 100644
--- a/tests/test_Btn.py
+++ b/tests/test_Btn.py
@@ -11,7 +11,7 @@ class TestBtn:
         btn = sw.Btn()
         assert btn.color == "primary"
         assert btn.v_icon.children[0] == ""
-        assert btn.children[1] == "Click"
+        assert btn.children[1] == ""
 
         # extensive btn
         btn = sw.Btn("toto", "fas fa-folder")
@@ -42,12 +42,18 @@ class TestBtn:
 
         assert isinstance(btn.v_icon, v.Icon)
         assert btn.v_icon.children[0] == gliph
+        assert btn.v_icon.left is True
 
         # change existing icon
         gliph = "fas fa-file"
         btn.gliph = gliph
         assert btn.v_icon.children[0] == gliph
 
+        # display only the gliph
+        btn.msg = ""
+        assert btn.children[1] == ""
+        assert btn.v_icon.left is False
+
         # remove all gliph
         gliph = ""
         btn.gliph = gliph
@@ -79,4 +85,4 @@ class TestBtn:
     def btn(self):
         """Create a simple btn"""
 
-        return sw.Btn()
+        return sw.Btn("Click")