Add a check for the correct version of powershell

[plastikfan]

Need to ensure that the user is running the minimum version of powershell and issue a warning message for them to upgrade.

The check would need to be performed at the import stage.

Under PS Version 5.1 these are the errors seen at import time (running in the old console):

At C:\shared\PowerShell\profile.shared.ps1:105 char:67
+ ...        $greeting = "� Restarted! (Pester Tag: '$env:tag' ✔�)";
+                                                                    ~~~
Unexpected token '�' in expression or statement.
At C:\shared\PowerShell\profile.shared.ps1:103 char:60
+         if (($tag -is [string]) -or ($tag -is [string[]])) {
+                                                            ~
Missing closing '}' in statement block or type definition.
At C:\shared\PowerShell\profile.shared.ps1:100 char:37
+       if (Test-Path -Path $tagPath) {
+                                     ~
Missing closing '}' in statement block or type definition.
At C:\shared\PowerShell\profile.shared.ps1:97 char:19
+     pwsh -Command {
+                   ~
Missing closing '}' in statement block or type definition.
At C:\shared\PowerShell\profile.shared.ps1:96 char:17
+   while ($true) {
+                 ~
Missing closing '}' in statement block or type definition.
At C:\shared\PowerShell\profile.shared.ps1:83 char:26
+ function restart-session {
+                          ~
Missing closing '}' in statement block or type definition.
At C:\shared\PowerShell\profile.shared.ps1:105 char:70
+ ...        $greeting = "� Restarted! (Pester Tag: '$env:tag' ✔�)";
+                                                                       ~
Unexpected token ')' in expression or statement.
At C:\shared\PowerShell\profile.shared.ps1:105 char:71
+ ...        $greeting = "� Restarted! (Pester Tag: '$env:tag' ✔�)";
+                                                                        ~~
The string is missing the terminator: ".
    + CategoryInfo          : ParserError: (:) [], ParseException
    + FullyQualifiedErrorId : UnexpectedToken