Use sentence case everywhere

We have not been good at consistent casing so far. Now we use 'Sentence case' everywhere. EVERYWHERE.

Also Removing 'Lc' prefix from i18n field names: the 'Lc' stood for lowercase but now that everything
is in 'Sentence case' there's no need for the distinction.

I've got a couple lower case things I've kept: namely, things that show up in parentheses.

pkg/integration/tests/commit/amend.go

@@ -26,7 +26,7 @@ var Amend = NewIntegrationTest(NewIntegrationTestArgs{
 			Press(keys.Commits.AmendToCommit)
 
 		t.ExpectPopup().Confirmation().Title(
-			Equals("Amend Last Commit")).
+			Equals("Amend last commit")).
 			Content(Contains("Are you sure you want to amend last commit?")).
 			Confirm()
 

pkg/integration/tests/commit/create_tag.go

@@ -25,7 +25,7 @@ var CreateTag = NewIntegrationTest(NewIntegrationTestArgs{
 
 		t.ExpectPopup().Menu().
 			Title(Equals("Create tag")).
-			Select(Contains("lightweight")).
+			Select(Contains("Lightweight")).
 			Confirm()
 
 		t.ExpectPopup().Prompt().

pkg/integration/tests/commit/new_branch.go

@@ -28,7 +28,7 @@ var NewBranch = NewIntegrationTest(NewIntegrationTestArgs{
 			Press(keys.Universal.New).
 			Tap(func() {
 				branchName := "my-branch-name"
-				t.ExpectPopup().Prompt().Title(Contains("New Branch Name")).Type(branchName).Confirm()
+				t.ExpectPopup().Prompt().Title(Contains("New branch name")).Type(branchName).Confirm()
 
 				t.Git().CurrentBranchName(branchName)
 			}).

pkg/integration/tests/commit/reset_author.go

@@ -29,7 +29,7 @@ var ResetAuthor = NewIntegrationTest(NewIntegrationTestArgs{
 			Tap(func() {
 				t.ExpectPopup().Menu().
 					Title(Equals("Amend commit attribute")).
-					Select(Contains("reset author")).
+					Select(Contains("Reset author")).
 					Confirm()
 			}).
 			Lines(

pkg/integration/tests/commit/revert_merge.go

@@ -26,7 +26,7 @@ var RevertMerge = NewIntegrationTest(NewIntegrationTestArgs{
 			Lines(
 				Contains("first change"),
 				Contains("second-change-branch unrelated change"),
-				Contains("cancel"),
+				Contains("Cancel"),
 			).
 			Select(Contains("first change")).
 			Confirm()

pkg/integration/tests/commit/set_author.go

@@ -32,7 +32,7 @@ var SetAuthor = NewIntegrationTest(NewIntegrationTestArgs{
 			Tap(func() {
 				t.ExpectPopup().Menu().
 					Title(Equals("Amend commit attribute")).
-					Select(Contains(" set author")). // adding space at start to distinguish from 'reset author'
+					Select(Contains(" Set author")). // adding space at start to distinguish from 'reset author'
 					Confirm()
 
 				t.ExpectPopup().Prompt().