Refactor ButtonLayout module components

- Rename ButtonLayout module to just Buttons

- Rename ButtonLayout into AutoDirectionLayout and move it to Base,
  it's useful not just for buttons

- Rename OtherButton into GroupButton, which is now the base of all
  other Buttons buttons

- Add generic (Positive|Middle|Negative)Button components, which are now
  the base for (Apply|Cancel)Button

src/gui/Pages/AddAccount/Register.qml

@@ -3,13 +3,13 @@
 import QtQuick 2.12
 import QtQuick.Layouts 1.12
 import "../../Base"
-import "../../Base/ButtonLayout"
+import "../../Base/Buttons"
 
 HFlickableColumnPage {
     function takeFocus() { registerButton.forceActiveFocus() }
 
 
-    footer: ButtonLayout {
+    footer: AutoDirectionLayout {
         ApplyButton {
             id: registerButton
             text: qsTr("Register from Riot")

src/gui/Pages/AddAccount/Reset.qml

@@ -3,13 +3,13 @@
 import QtQuick 2.12
 import QtQuick.Layouts 1.12
 import "../../Base"
-import "../../Base/ButtonLayout"
+import "../../Base/Buttons"
 
 HFlickableColumnPage {
     function takeFocus() { resetButton.forceActiveFocus() }
 
 
-    footer: ButtonLayout {
+    footer: AutoDirectionLayout {
         ApplyButton {
             id: resetButton
             text: qsTr("Reset password from Riot")

src/gui/Pages/AddAccount/SignIn.qml

@@ -3,7 +3,7 @@
 import QtQuick 2.12
 import QtQuick.Layouts 1.12
 import "../../Base"
-import "../../Base/ButtonLayout"
+import "../../Base/Buttons"
 
 HFlickableColumnPage {
     id: page
@@ -77,7 +77,7 @@ HFlickableColumnPage {
     }
 
 
-    footer: ButtonLayout {
+    footer: AutoDirectionLayout {
         ApplyButton {
             enabled: page.canSignIn
             text: qsTr("Sign in")