A directory-category for terminal emulators

This is a mostly cosmetical commit, in the sense it doesn't change the contents
of any package, but reorganizes the overall Nixpkgs expressions.

Terminal emulators are an ubiquitous tool for any Unix user; even the beginners
are routinely familiarized to it. And, manifestly, there are many
implementations of terminal emulators out there, from those traditionally made
in C and C++ to those written in Haskell and Go.

Terminal emulators deserve more highlight. This commit does that by creating a
category for them.

pkgs/applications/terminal-emulators/wayst/utf8proc.patch

@@ -0,0 +1,24 @@
+commit caa5a6bed31937f2d1b322da204e11eae57a720f
+Author: Nicolas Berbiche <nicolas@normie.dev>
+Date:   Tue Oct 20 18:14:44 2020 -0400
+
+    PATCH: use nixpkgs utf8proc
+    
+    This patch forces the Makefile to use utf8proc from `buildInputs`.
+    The Makefile relies on ldconfig to find the utf8proc libraries,
+    which is not possible with nixpkgs.
+
+diff --git a/Makefile b/Makefile
+index caccdf7..90b11ea 100644
+--- a/Makefile
++++ b/Makefile
+@@ -29,7 +29,7 @@ else
+ 	LDFLAGS = -O2 -flto
+ endif
+ 
+-ifeq ($(shell ldconfig -p | grep libutf8proc.so > /dev/null || echo fail),fail)
++ifeq (false,fail)
+ $(info libutf8proc not found. Support for language-specific combining characters and unicode normalization will be disabled.)
+ 	CFLAGS += -DNOUTF8PROC
+ else
+