indicate stash with symbols

Like already in place for the branch, Unicode symbols or letter
indicators make it easier to tell the stash counter apart from other
segments.

powerline/config_files/themes/ascii.json

@@ -15,6 +15,9 @@
 		"branch": {
 			"before": "BR "
 		},
+		"stash": {
+			"before": "ST "
+		},
 		"cwd": {
 			"args": {
 				"ellipsis": "..."

powerline/config_files/themes/powerline.json

@@ -14,6 +14,9 @@
 		"branch": {
 			"before": " "
 		},
+		"stash": {
+			"before": "⌆ "
+		},
 		"cwd": {
 			"args": {
 				"ellipsis": "⋯"

powerline/config_files/themes/powerline_unicode7.json

@@ -14,6 +14,9 @@
 		"branch": {
 			"before": "🔀 "
 		},
+		"stash": {
+			"before": "📝"
+		},
 		"cwd": {
 			"args": {
 				"ellipsis": "⋯"

powerline/config_files/themes/unicode.json

@@ -14,6 +14,9 @@
 		"branch": {
 			"before": "⎇ "
 		},
+		"stash": {
+			"before": "⌆"
+		},
 		"cwd": {
 			"args": {
 				"ellipsis": "⋯"

powerline/config_files/themes/unicode_terminus.json

@@ -14,6 +14,9 @@
 		"branch": {
 			"before": "BR "
 		},
+		"stash": {
+			"before": "ST "
+		},
 		"cwd": {
 			"args": {
 				"ellipsis": "…"

powerline/config_files/themes/unicode_terminus_condensed.json

@@ -14,6 +14,9 @@
 		"branch": {
 			"before": "B "
 		},
+		"stash": {
+			"before": "S "
+		},
 		"cwd": {
 			"args": {
 				"use_path_separator": true,