feat(wm): allow resize-axis for custom primary col

This commit allows the resize-axis cmd on Axis::Horizontal to operate on
the Primary column of a CustomLayout.

Note that this will only operate on a CustomLayout that has met the
window count threshold to enable the tertiary column. If it has not, the
layout will render as DefaultLayout::Columns, which does not support the
resize-axis cmd.

Cargo.lock

@@ -96,6 +96,7 @@ dependencies = [
  "os_str_bytes",
  "strsim",
  "termcolor",
+ "terminal_size",
  "textwrap",
  "unicase",
 ]
@@ -1197,12 +1198,23 @@ dependencies = [
  "winapi-util",
 ]
 
+[[package]]
+name = "terminal_size"
+version = "0.1.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "633c1a546cee861a1a6d0dc69ebeca693bf4296661ba7852b9d21d159e0506df"
+dependencies = [
+ "libc",
+ "winapi 0.3.9",
+]
+
 [[package]]
 name = "textwrap"
 version = "0.14.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0066c8d12af8b5acd21e00547c3797fde4e8677254a7ee429176ccebbe93dd80"
 dependencies = [
+ "terminal_size",
  "unicode-width",
 ]