mainview: change about jami button from Button to MaterialButton

Gitlab: #139
Change-Id: I55bfbc8a7f404cad917f462e5e77c793747fbc21

src/constant/JamiStrings.qml

@@ -375,6 +375,7 @@ Item {
     property string errorCreateAccount: qsTr("Error while creating your account. Check your credentials.")
     property string createNewRV: qsTr("Create new rendezvous point")
     property string createNewJA: qsTr("Create a Jami account")
+    property string aboutJami: qsTr("About Jami")
 
     // Smart list context menu
     property string declineContactRequest: qsTr("Decline contact request")

src/mainview/components/WelcomePage.qml

@@ -46,7 +46,7 @@ Rectangle {
                 Layout.alignment: Qt.AlignCenter
                 Layout.preferredWidth: welcomeRectComponentsGroup.width
                 Layout.preferredHeight: 100
-                Layout.topMargin: 32
+                Layout.topMargin: JamiTheme.preferredMarginSize
                 Layout.bottomMargin: 10
 
                 smooth: true
@@ -97,7 +97,7 @@ Rectangle {
                 Layout.alignment: Qt.AlignCenter
                 Layout.preferredWidth: welcomeRectComponentsGroup.width
                 Layout.preferredHeight: 65
-                Layout.bottomMargin: 5
+                Layout.bottomMargin: JamiTheme.preferredMarginSize
 
                 visible: AccountAdapter.currentAccountType === Profile.Type.RING
 
@@ -144,21 +144,22 @@ Rectangle {
         }
     }
 
-    Button {
-        id: btnAbout
+    MaterialButton {
+        id: btnClose
 
         anchors.bottom: parent.bottom
-        anchors.bottomMargin: 10
+        anchors.bottomMargin: JamiTheme.preferredMarginSize
         anchors.horizontalCenter: parent.horizontalCenter
 
-        background: Rectangle {
-            color: "transparent"
-        }
+        width: 150
+        height: 30
 
-        contentItem: Text {
-            text: qsTr("About Jami")
-            color: "grey"
-        }
+        color: JamiTheme.buttonTintedBlack
+        hoveredColor: JamiTheme.buttonTintedBlackHovered
+        pressedColor: JamiTheme.buttonTintedBlackPressed
+        outlined: true
+
+        text: JamiStrings.aboutJami
 
         onClicked: aboutPopUpDialog.open()
     }